[Frontiers in Bioscience 18, 394-421, January 1, 2013]

Prognostic significance and targeting of HER family in colorectal cancer

Said Abdullah Khelwatty1, Sharadah Essapen2, Alan Michael Seddon1, Helmout Modjtahedi1

1School of Life Sciences, Kingston University London, Kingston, UK, 2St Luke's Cancer Centre, Royal Surrey County NHS Foundation Trust, Guildford, Surrey, UK

TABLE OF CONTENTS

1. Abstract
2. Introduction
3. The type I growth factor receptors and their ligands
3.1. Expression pattern and prognostic significance of EGFR and its ligands in colorectal cancer
3.2. Expression pattern and prognostic significance of HER-2 in colorectal cancer
3.3. Expression pattern and prognostic significance of HER-3 and HER-4 in colorectal cancer
4. Targeting of HER family members in colorectal cancer.
4.1. EGFR targeted therapy
4.1.1. Anti-EGFR mAbs
4.1.1.1. Cetuximab
4.1.1.2. Panitumumab
4.1.1.3. Necitumumab (IMC-11F8)
4.1.1.4. Other anti-EGFR mAbs
4.1.2. EGFR Tyrosine kinase inhibitors
4.1.2.1. Gefitinib
4.1.2 2. Erlotinib
4.2. HER-2 and HER-3 targeted therapy
4.2.1. Trastuzumab
4.2.2. MM-121
4.3. Dual and Pan-HER inhibitors of ErbB family members
4.3.1. Lapatinib
4.3.2. Afatinib
4.3.3. HM781-36B
4.3.4. Other anti-HER inhibitors
5. Predictive markers for response or resistance to therapy to HER inhibitors in colorectal cancer
5.1. Predictive value EGFR protein expression measured by IHC
5.2. Predictive value of EGFR mutations and EGFR gene amplification
5.3. Predictive value of EGFR ligands
5.4. Predictive value of downstream cell signalling pathways
5.4.1. KRAS
5.4.2. B-RAF
5.4.3. PI-3K
5.4.4. PTEN
5.5. Predictive value of IGF-IR and other heterologous receptors
6. Perspectives
7. Acknowledgement
8. References

1. ABSTRACT

Colorectal cancer is one of the leading causes of cancer deaths. At present, anti-epidermal growth factor receptor (EGFR) monoclonal antibodies (mAbs) cetuximab and panitumumab and anti-vascular endothelial growth factor (VEGF) mAb bevacizumab have been incorporated into treatment paradigms for patients with refractory metastatic colorectal cancer. However, many patients simply do not respond to these treatments or eventually acquire resistance following a short course therapy. In this article, we review the literature for studies on the expression patterns, prognostic significance and predictive value of HER (also called erbB) family members and other factors for response to therapy with the HER inhibitors in colorectal cancer. We discuss some of the advances, challenges as well as future opportunities for more effective targeting of the HER receptors using a cocktail of HER inhibitors (e.g. dual and pan HER TKIs, monospecific or bispecific antibodies) in combination with other therapeutic interventions.

2. INTRODUCTION

Despite major advances in the diagnosis, treatment and management of cancer patients, colorectal cancer is still a major health problem worldwide. In 2008, colorectal cancer was estimated to be the third most commonly diagnosed cancer (1.23 million) and the fourth leading cause of cancer deaths (608,000) worldwide (1). However, there are worldwide variations for both the incidence rates and mortality rates of colorectal cancer. The highest incidence rates for colorectal cancer are located in North America and Europe and the lowest rates in countries in Asia, Africa and South America (2). In 2012, colorectal cancer is estimated to be the fourth most commonly diagnosed cancer (143,460) but the second leading cause of cancer deaths (51,690) after lung cancer in the USA (3) . Although colorectal cancer diagnosed at an early stage has 5 year survival of about 90%, the majority of colorectal cancer patients are diagnosed with locally advanced or metastatic disease and have a poor response to conventional forms of therapy with a 5 year survival rates of 68% and 10% respectively (4, 5). Therefore, it is of prime importance to discover more specific biological and molecular markers that could be used not only for the early detection of colorectal cancer, but also to investigate their importance as prognostic indicators, predictive factors and therapeutic targets.

In the past forty years, metastatic colorectal cancer has been treated with fluoropyrimidine-based chemotherapy and more recently, drugs such as irinotecan and oxaliplatin have been introduced to this already established chemotherapeutic regimen. Although these treatments have increased time to progression and improved overall survival, they have certain drawbacks and adverse effects (6, 7). For example, one of the major limitation of these regimens is the non-specificity of the treatment which ultimately may cause various haematological disorders and increase the risk of infections (8). In the past twenty years, due to a better understanding of tumour biology and following demonstration of the aberrant expression and activation of growth factor receptor system in a variety of human tumours, there have been major initiatives in targeted therapy of human cancers using monoclonal antibody (mAb) based products and small molecule tyrosine kinase inhibitors (TKIs). Of several monoclonal antibody based drugs, anti-epidermal growth factor receptor (EGFR) mAbs cetuximab and panitumumab and anti-vascular endothelial growth factor (VEGF) mAb bevacizumab have been approved for the treatment of patients with refractory metastatic colorectal cancer (9-12). In this article, we will review the literature for studies on the expression patterns, prognostic significance and predictive value of the HER family members for response to therapy with HER inhibitors in colorectal cancer. We will discuss some of the advances and challenges together with future opportunities for the identification of a more specific population of colorectal cancer patients who are most likely to benefit from therapy with the HER inhibitors in combination with other therapeutic interventions.

3. THE TYPE I GROWTH FACTOR RECEPTOR AND THEIR LIGANDS

The type I growth factor receptor family of tyrosine kinases, also known as the ErbB or HER family, consists of four members namely EGFR (HER-1, ErbB-1), HER-2 (neu, ErbB-2), HER-3 (ErbB-3) and HER-4 (ErbB-4) (13-15). Of these, EGFR and HER-2 are the most extensively studied and best understood receptors in this family. The EGFR can be activated following the binding of several ligands such as epidermal growth factor (EGF), transforming growth factor alpha (TGFα), amphiregulin (AR), Heparin-binding betacellulin (BTC), and epiregulin (EPI) to its extracellular domain (16, 17). The binding of the cognate ligands to the external domain of the receptor induces the formation of homo- or hetero-dimers between different members of the HER family causing autophosphorylation of numerous tyrosine residues in its intracellular domain and ultimately the activation of the downstream signalling molecules such as the Ras, Raf, mitogen activated protein kinase (MAPK) cell proliferation pathways and the phosphatidylinositol 3 kinase (PI-3K)/Akt cell survival pathway (18) (Figure 1). Although MAPK and PI-3K/Akt pathways are the two major and most studied pathways activated by the EGFR, other pathways such as janus kinase and signal transducer and activator of transcription (JAK/STAT) and phospholipase C (PLC-γ)/Ca2+/calmodulin-dependant kinases are also activated by EGFR and other members of the HER family (14). In the past few years, the role of the MAPK pathway in colorectal cancer has been studied extensively and in most studies K-RAS and B-RAF mutations have been associated with poor response to therapy with anti-EGFR mAbs and shorter survival and shorter progression free survival in patients with colorectal cancer (19). The biological consequences of EGFR activation include increased cell proliferation, reduced apoptosis, increased angiogenesis, migration, invasion and resistance to chemotherapy and radiotherapy which are the hallmarks of human cancer (20-26).

In the past 40 years, the aberrant expression and activation of different members of the HER family have been reported in a variety of human tumours and in some studies have been associated with resistance to the conventional forms of therapy and a poorer prognosis (27, 28) (also see Eccles et al. and Ioannou et al. in this issue). The aberrant activation of HER family members can be due to several mechanisms including mutations in the intracellular or extracellular domains of the receptor, overexpression of the wild-type receptor, overproduction of autocrine and paracrine ligands, homodimerisation and heterodimerisation between different members of the HER family or activation by a heterologus receptor such as IGF-IR (14, 29-36). In addition to the traditional pathways of HER signalling, several studies have reported the presence of intact HER family members such as EGFR, as a transcription factor, in the nucleus of proliferating normal and cancer cells. For example, nuclear EGFR has been detected in a number of human cancers including breast, bladder, pancreatic and colorectal, and nuclear expression of the EGFR has been associated with acquired resistance to therapy, tumour aggressiveness and poor survival (37-43). This demonstrates the complex mechanisms by which HER signalling may be activated and the need for further studies to unravel the role of nuclear HER family members in the proliferation and progression of tumour cells as wells as its potential as a prognostic marker, predictive biomarker and therapeutic target in colorectal cancer patients (39, 40, 44-47).

3.1. Expression pattern and prognostic significance of EGFR and its ligands in colorectal cancer

The expression of EGFR has been reported in patients with colorectal cancer but ranges from 8 to 100% of cases examined (48-51) (Table 1). In one of the earliest studies Mayer et al. determined EGFR expression using immunohistochemistry (IHC) in 82 Dukes' A-D colorectal cancer patients and found a positive EGFR expression in 97.6% of the cases examined (51). Similarly, in another key study, Spano and colleagues determined EGFR expression by IHC in 150 colorectal cancer patients and found EGFR reactivity and EGFR over-expression in 97% and 80% of the cases respectively (49). In another study, Frattini and colleagues investigated EGFR over-expression by IHC and fluorescence in situ hybridisation (FISH) in 27 metastatic colorectal cancer patients and they found a positive EGFR expression in 100% (IHC) and 30% (FISH) of the cases examined (50) (Table 1). On the other hand, other studies have found the expression of EGFR in colorectal cancer to be much lower. Ooi and colleagues examined EGFR expression in a large cohort of 244 stage 0-IV colorectal cancer patients using IHC but found EGFR positive tumours in only 8% of the cases examined (48). In other studies, the EGFR status of the tumour was determined by measuring the EGFR gene copy number (GCN) and/or IHC. The EGFR GCN was determined using FISH, chromogenic in situ hybridisation (CISH) and polymerase chain reaction (PCR). The expression of EGFR GCN for colorectal cancer also exhibits wide variation, ranging from 6 to 59% of the cases examined (52, 53) (Table 1). In one study, tumour specimens from 147 primary and metastatic colorectal cancer patients were examined for the expression of both EGFR protein and EGFR GCN. EGFR protein positive tumour was found in 85% and 79% of primary and metastatic colorectal cancer cases examined but EGFR gene amplification was detected in 12% of primary and 8% of metastatic cancer cases respectively. Interestingly, all tumours that were negative for EGFR protein were also negative for EGFR gene amplification (54) (Table 1). Moreover, in one of the largest and most recent study's to date, Jolien and colleagues investigated EGFR expression in 755 metastatic colorectal cancer patients using PharmDx kit and FISH. Tumours were considered EGFR positive when the membranous EGFR staining was present in more than 1% of tumour cells. They found 61.7% and 15.3% of the cases to be EGFR positive and to have EGFR gene amplification respectively (55). In contrast, the results of another study involving 101 metastatic colorectal cancer patients showed a higher percentage of the patients with both EGFR GCN amplification (59%) and expression of the EGFR protein (89%) (53) (Table 1). Some of the contributing factors for such a wide variation in the percentage of EGFR positive colorectal cancer cases could be the use of different anti-EGFR antibodies, different scoring system, different patient subpopulations and the small number of patients in some studies (33, 56, 57) (Table 1).

In some studies, the EGFR expression or increased gene copy number have been associated with a poor prognosis and other established prognostic indicators in colorectal cancer (49, 51, 58, 59) (Table 1). For example, in one study, Kluftinger and colleagues investigated the prognostic significance of EGFR in 32 colorectal cancer patients and found 44% of the cases to be EGFR positive and EGFR expression was associated with more advanced tumours and lympho-vascular invasion (p < 0.05) (58). In another study, Galizia et al. determined EGFR expression in 154 Dukes A-D colorectal cancer patients and found a significant association between EGFR expression and tumour node metastases (p = 0.003), nodal status (p = 0.025), presence of distant metastases (p = 0.004) and Dukes' stage (p = 0.001). They also found that colon cancer cells which had metastasized to a distant site expressed up to five times more EGFR mRNA when compared to Dukes' A tumour cells (59). More recently, in another study involving 386 stage I-IV colorectal cancer patients the variation in EGFR expression within tumours was investigated, comparing central parts to the invasive margin (60). The study found positive EGFR immunostaining in 46% of the central part compared with 58% in the invasive margins of the primary tumours. The increased score at the invasive margin compared to central parts of the tumours was found in 25% of the cases examined and was associated with a more aggressive behaviour and led to a survival disadvantage (60). In contrast, other studies did not find any association between the EGFR expression and prognosis (61-64). For example, McKay and colleagues examined tumour specimens from 249 Dukes' C and D colorectal cancer patients. While tumour specimens from 72.7% of the patients were EGFR positive, they did not find any significant association between the EGFR expression and overall survival. In addition, EGFR expression in primary and metastatic tumours was not significantly different (65). In another study, Yamada and colleagues determined the EGFR and AR expression in tumour specimens from 106 primary colorectal cancers and 16 metastatic liver lesions. They found 12.3% and 54.7% of the primary lesions to be AR and EGFR positive respectively. Interestingly, 81.6% of metastatic liver cancer cases were AR positive and AR expression in the primary colorectal cancer was found to be a predictive biomarker of liver metastasis (66). More recently, Kuramochi and colleagues examined AR and EPI mRNA expression level in tumour specimens from 120 colorectal cancer patients with liver metastasis (100 with synchronous metastasis, 20 with metachronous). They found a modest correlation between the AR and EPI expression in the primary tumour and liver metastasis but no significant survival difference between patients with low or high AR and EPI expression. However, in multivariate analysis, low EPI expression was found to be significantly associated with better overall survival in patients who never received anti-EGFR therapy (67) (Table 1).

Despite such a wide variation in the percentage of EGFR positive cases reported in the literature, the extracellular domain of EGFR is an ideal therapeutic target for anti-EGFR antibodies and IHC is the most commonly used method for the evaluation of the EGFR expression level and its cellular location. However, the lack of a uniform scoring system, the use of different antibodies, different patient populations and, as has already been noted, the small number of patients in some studies are considered to be some of the contributory factors for the wide variation reported for the expression pattern and percentage of EGFR positive cases in patients with colorectal cancer and the conflicting data on its prognostic significance (33) (Table 1). Therefore, in order to resolve the conflicting data on the expression pattern and prognostic significance of EGFR in patients with colorectal cancer, it is essential to conduct more detailed studies on the expression level of the EGFR ligands, various forms of EGFR (e.g. wild-type, mutated, soluble, phosphorylated EGFR) and their cellular locations (e.g. cytoplasmic, membranous or nuclear) and such studies should be conducted on a larger group of patients using a standard scoring system (39, 40, 44, 56, 68-71).

3.2. Expression pattern and prognostic significance of HER-2 in colorectal cancer

The human epidermal growth factor receptor-2 (HER-2), also known as neu or c-erb-2, is the second most extensively studied and understood member of the HER family. Many studies have shown the aberrant expression of HER-2 in a variety of human tumours including breast cancer and the anti-HER-2 antibody trastuzumab (Herceptin) has already been approved for the treatment of patients with HER-2 overexpressing early stage and metastatic breast cancer as well as in patients with metastatic stomach cancer (72, 73).

Several studies have reported the overexpression of HER-2 in colorectal cancer (74-76) (Table 2). However, like the expression pattern of EGFR described above, there is also a wide variation in the expression level of HER-2 reported in patients with colorectal cancer. For example, in one study involving 146 Dukes' B patients, HER-2 expression was demonstrated in 70% of the colorectal cancer cases (77). Similarly, Kruszewski et al. determined the expression levels of HER-2 in 202 colorectal cancer patients with 66% (cytoplasmic) and 27% (membranous) of the cases being HER-2 positive (78). In another study, Kavanagh and colleagues examined tumour specimens from 132 Dukes' A-D colorectal cancer patients and tumour specimens from 13.6% of the patients were HER-2 positive (79). More recently however, Wei and colleagues examined tumour specimens from 60 primary node positive colorectal cancer cases and found HER-2 expression to be rare (1.8%) in such patients (80) Table 2).

In the past two decades, several studies have also investigated the prognostic significance of HER-2 in patients with colorectal cancer (76, 78, 79, 81, 82). In one study, Essapen and colleagues examined 170 archival specimens of Dukes' B and C colorectal cancer using IHC and 87% of the cases showed cytoplasmic staining, but only 2% showed membranous staining for HER-2. Positive cytoplasmic immunostaining was found to be associated with a significantly better overall survival (HR 0.46, CI95 0.24-0.87) in the Dukes C cancers, but no survival benefit was seen in the Dukes' B cancers (81). In another study, Antonacopoulou et al. examined 124 stage I-IV colorectal cancer patients for the expression of HER-2. Tumours were considered HER-2 positive when there was only membranous reactivity. Based on this criteria, they found 27.4% of the cases to be HER-2 positive and HER-2 expression was associated with shorter survival (83). In contrast, other studies did not find any association between HER-2 expression and survival (64, 79) (Table 2). For example, in one study involving 132 Dukes' A-D colorectal cancer patients, there were no significant associations between HER-2 positivity and gender, age, grade, Dukes' stage, TNM stage, time to recurrence and 5 year survival. Moreover, HER-2 gene amplification did not correlate with the established prognostic indicators (79). In addition, in the study by Kruszewski and colleagues described above, they also did not find any correlation between either membranous or cytoplasmic expression of HER-2 and colorectal cancer patients survival (78) (Table 2).

3.3. Expression pattern and prognostic significance of HER-3 and HER-4 in colorectal cancer

The third and fourth members of the type I growth factor receptor family, HER-3 and HER-4 are found in many organs such as the stomach, lung, pancreas, and breast and they are known to play a key role in various pathological processes including cancer (84-87). However, in the past 2 decades, there have been very few studies on the expression level of HER-3 and HER-4 in colorectal cancer. As with the results from the studies noted above on the expression of EGFR and HER-2, the expression of HER-3 reported in colorectal cancer also exhibits wide variation, ranging from 16 to 89% of the cases examined (80, 88-91) (Table 3). In one study, Maurer et al. examined tumour specimens from 35 colorectal cancer patients and found 89% of the cases to be HER-3 positive (88). In contrast, other studies have found a lower percentage of HER-3 positive colorectal cancer cases. For example, Wei and colleagues determined HER-3 expression by IHC in 60 colorectal cancer patients and found only 16% of the primary tumours to be HER-3 positive (80).

The expression of HER-4 in colorectal cancer ranges from 11 to 81% of the cases examined (64, 85, 89, 92) (Table 3). However, there are a limited number of studies on the prognostic significance of HER-3 and HER-4 or co-expression of all members of the HER family in colorectal cancer (64, 85, 89, 91, 92) (Table 3). Kapitanović and colleagues examined HER3 expression in 55 Dukes A-C cancer patients and found patients whose tumours were HER-3 negative had a significantly longer survival (Kapitanović et al., 2000). In contrast, Baiocchi et al. found an association between negative HER-3 expression and lymphovascular invasion and a poorer overall survival (64). There are also conflicting data on the expression of HER-3 at different stages of colorectal cancer and, as noted above for the other HER family members, it is suggested that such differences could be due to the usage of different antibodies, different scoring systems as well as differences in the number of patients at different stages of the disease (89, 92).

In the case of HER-4, there have only been four studies on its expression pattern and prognostic significance in patients with colorectal cancer to date (64, 85, 89, 92) (Table 3). In addition, only three studies have examined the expression of all members of the HER family in colorectal cancer (64, 89, 92) (Table 3). In 2002, Lee and colleagues compared the expression levels of all HER family members in 125 Dukes' A-D colorectal cancer cases and did not find overexpression of any of the HER family members alone to be significantly associated with shorter overall survival, but simultaneous overexpression of HER-2 and HER-4 was found to be significantly associated with a poorer overall survival (89). Baiocchi et al. examined 109 stage II-III colorectal cancer patients for the expression levels of HER-1 to HER-4. Interestingly, their study found membranous positive HER-4 expression as an independent prognostic factor for recurrence, while HER-3 negative expression was an independent prognostic factor for recurrence and poorer survival in the multivariate analysis(64). In addition, Ljuslinder and colleagues investigated the difference between the expression of HER1 to HER4 in primary and metastatic sites of 64 stage I-III colorectal cancer patients. They did not find any significant differences between HER-2, HER-3 and HER-4 expressions in primary and metastatic sites. Interestingly, while HER-3 and HER-4 co-expression was found to be significantly higher in late stage tumours, EGFR expression was lost in metastatic sites (92). More recently, we determined the expression level of all HER family members in a large panel of human colorectal tumour cell lines and found significant association between the co-expression of EGFR, HER-2 and HER-3 and response to treatment with an irreversible pan-HER blocker, afatinib (P = 0.021) (93).

The wide variation in the expression level of the HER family members reported in the literature in patients with colorectal cancer, as well as the limited number of studies on the expression level of all members of HER family and their ligands, warrant further investigations on the expression patterns and prognostic significance of all forms of HER family members and their ligands in both primary and metastatic lesions and such studies should ideally be conducted on a larger group of colorectal cancer patients.

4. TARGETING OF HER FAMILY MEMBERS IN COLORECTAL CANCER

4.1. EGFR targeted therapyIn the past two decades, there has been a rapid increase in the targeted therapy of human cancers. In particular, aberrant expression and activation of EGFR in a variety of tumours has stimulated the development of several EGFR inhibitors for use in cancer therapy. Of these, anti-EGFR mAbs cetuximab and panitumumab have already gained the approval of the US Food and Drugs Administration (FDA) for the treatment of patients with metastatic colorectal cancer in combination with chemotherapy (9, 10, 50, 52, 94-100). Small molecule TKIs have been extensively studied in colorectal cancer and in addition have been approved for treatment of patients with non-small cell lung cancer (gefitinib and erlotinib) and pancreatic cancer (erlotinib) (101-103). There are many other types of EGFR inhibitors including the dual EGFR/HER-2 TKI and pan HER TKIs that are at different stages of preclinical and clinical evaluations and some of these will be discussed here (Table 4).

4.1.1. Anti-EGFR mAbs

4.1.1.1. Cetuximab (Erbitux®)

Cetuximab is an IgG1 chimeric monoclonal antibody that binds selectively to the external domain of EGFR and inhibits binding of the ligands to the receptors (9, 104), (also see Fan et al. in this issue). This in turn prevents the activation of the receptor's tyrosine kinase activity and downstream cell signalling pathways (9). Since cetuximab is an IgG1 antibody, it can also induce anti-tumour activity in vivo by mediating antibody dependent cellular cytotoxicity (ADCC) and complement dependent cytotoxicity (CDC) (also see Fan et al. in this issue).

The pivotal BOND trial conducted by Cunningham and colleagues highlighted the benefit of cetuximab in chemo-refractory disease (94). This study included 329 randomly selected patients with disease progression during or within 3 months after treatment with irinotecan. The patients were subsequently randomised into two groups of 218 patients receiving combination therapy with cetuximab and irinotecan and 111 patients for cetuximab monotherapy. The study found the overall response rate in the intention-to-treat population to be 22.9% in combination therapy versus 10.8% found in the monotherapy group (P=0.007). The median time to progression was also noted to be longer in patients receiving the combination therapy of both drugs at 4.1 months compared to 1.5 months for those receiving cetuximab alone. However, there was no significant difference in the median overall survival rate (8.6 months versus 6.9 months, P=0.48). There were no significant adverse reactions to the combination therapy reported in this study. However, in 4 of the 329 patients severe anaphylactic reactions to cetuximab were noted and the treatment was stopped. In December 2004, as a result of the BOND data, cetuximab gained approval by the FDA for use in metastatic colorectal cancer patients whose tumours were refractory to irinotecan based therapy (9). Recent studies have shown that the effectiveness of cetuximab is limited to those patients whose tumours express wild-type k-RAS. In approximately 40% of colorectal cancer cases KRAS is found to have a mutation which is associated with poor prognosis (105).

The addition of cetuximab to standard chemotherapy in patients with k-RAS wild type metastatic liver disease secondary to colorectal cancer, can lead to a significantly increased response rate, leading to an increased liver resection rate. The CELIM study (106) was a randomised phase II study which compared tumour response and resectability rates in patients with initial unresectable liver metastases, treated with standard chemotherapy with or without cetuximab. The response rate for tumours was significantly higher with the addition of cetuximab in the k-RAS wild-type group versus the mutant k-RAS group (70% vs 41%, p=0.008). This translated into a higher resection rate of liver metastases from 32% at baseline to 60% after chemotherapy (p<0.0001). This study confirmed the increased response rates, reported by other investigators, with the addition of cetuximab to either FOLFOX or FOLFIRI standard chemotherapy. The CRYSTAL trial (107) randomised 1217 patients to FOLFIRI with or without cetuximab as first line treatment for metastatic colorectal cancer. This group confirm the findings of previous studies (94) of significantly improved median progression free survival with the addition of cetuximab (8.9 months versus 8 months for FOLFIRI alone). Furthermore, the study also noted a higher objective response rate (47% versus 39%) in patients treated with cetuximab in combination to FOLFIRI compared to FOLFIRI alone. However, the benefit was observed in patients with liver only metastases. Moreover, further studies such as the EPIC trial conducted by Sobrero et al. (108) evaluated the role of cetuximab in patients previously untreated with irinotecan and further in the first line metastatic setting. The study randomised 1298 EGFR-positive patients failing an oxaliplatin based first line regimen to either irinotecan or cetuximab combined with irinotecan. As a result, study found significant improvement in progression free survival with the combination compared to the single agent therapy of irinotecan (3.9 months versus 2.56 months). In addition, response rates were also noted to be significantly higher at 16% compared to 4% in patients treated with irinotecan alone.

In August 2009, NICE (UK) agreed to the use of cetuximab in addition to either FOLFOX or FOLFIRI chemotherapy in patients with liver metastases only, whose tumours are k-RAS wild-type, and in whom the metastases cannot be surgically removed, without significant down staging with primary chemotherapy.

4.1.1.2. Panitumumab (Vectibix®)

Unlike the chimeric IgG1 anti-EGFR mAb cetuximab, panitumumab is a fully human anti-EGFR mAb of IgG2 subclass (109, 110) (Table 2). As a result of a large, multinational, randomised, open label study conducted by Van Cutsem et al. panitumumab was approved by the US FDA for the treatment of metastatic colorectal cancer that is refractory to 5-Flouraracil, oxaliplatin, and irinotecan based regimens. This phase III study included 463 patients, treated with panitumumab plus best supportive care (BSC) (231 patients) or BSC alone (232 patients). The study reported a 46% reduction in the relative progression rate of the disease compared to the patients receiving only BSC. In addition, mean progression free survival time was higher in those receiving panitumumab than BSC alone (13.8 weeks versus 8.5 weeks), while no significant difference in overall survival between the groups were observed (111).

In 2007, Hecht et al. conducted a multicenter, non- randomised phase II study. The study included 148 patients with metastatic colorectal cancer refractory to fluoropyrimidines, oxaliplatin, and/or irinotecan. The patients were stratified into two groups according to staining intensity of high and low EGFR positivity (105 and 43 respectively). The study reported overall response of 9%, and stable disease was observed in 29% of patients, while progression free survival was 14 weeks and median overall survival being 9 months (112). In addition, several studies have evaluated the role of panitumumab in combination with other classic chemotherapy regimens as first-line treatment in metastatic colorectal cancer. However, the data available is limited as most of these studies are still ongoing. The PRIME study is one such study conducted by Siena et al. (113). It is the first phase III study to investigate the role of panitumumab in combination with FOLFOX4 as first-line treatment in metastatic colorectal cancer. The study enrolled 1,150 untreated patients randomised into two groups to receive panitumumab plus FOLFOX4 or FOLFOX4 alone. Progression free survival was the study's primary endpoint. In a pooled safety analysis, 903 patients were treated, with neutropenia (28%) and diarrhoea (11%) being the two most common adverse effects of the treatment. In addition, 93 patients (10%) reported a grade 3 skin reaction and only 3 patients experienced a grade 4 skin reaction. Similarly, in another ongoing multicenter phase III study the role of panitumumab in addition to FOLFIRI as a second-line treatment is being investigated (114). The study included 1,100 patients previously treated with only one fluoropyrimidine based chemotherapy regimen for metastatic colorectal cancer randomised into two groups receiving panitumumab plus FOLFIRI or FOLFIRI alone. The findings of the preliminary safety yet again identified neutropenia (15%) and diarrhoea (9%) to be the two most common adverse effects. Furthermore, 12% of the patients reported a grade 3 skin reaction while grade 4 skin toxicities were seen in <1% of the patients.

4.1.1.3. Necitumumab (IMC-11F8)

IMC-11F8 is another fully human anti-EGFR mAb. The mechanism of action of IMC-11F8 is similar to that of cetuximab. Interestingly, while both cetuximab and IMC-11F8 bind to the same domain with the same binding affinity, IMC-11F8 has been found to have similar anti-tumour potency but fewer side effects in comparison (115, 116). IMC-11F8 has been shown to block the phosphorylation of EGFR and MAPK in several tumour cell lines. The activity and efficacy of IMC-11F8 has been evaluated in various in vivo models including colon human tumour xenografts in athymic mice. Treatment with IMC-11F8 caused a dose dependent growth inhibition of tumours in mice models. In addition, combination of IMC-11F8 with irinotecan was found to have a superior anti-tumour effect in colon xenograft models (DLD-1, GEO, HT29) (117). More recently, a phase I study of sixty patients with advanced solid malignancies treated with IMC-11F8 found the antibody to be well tolerated and a partial response and stable disease was noted in 2 and 16 patients respectively (116). It is currently in phase II clinical trials in patients with metastatic colorectal cancer patients (NCT00835185).

4.1.1.4 Other anti-EGFR mAbs

Several other anti-EGFR mAbs (e.g. nimotuzumab, ICR62) have also been produced which are at different stages of pre-clinical and clinical evaluations (Table 4). ICR62 is a rat IgG2b anti-EGFR mAb and has been raised against the extracellular domain of the EGFR on a breast carcinoma cell line. MAb ICR62 was shown to be very effective in 1) inhibiting the binding of EGFR ligands (e.g. EGF, TGFα, HB-EGF, betacellulin, epiregulin) to the receptor, 2) blocking the ligand-induced tyrosine phosphorylation of the EGFR, 3) inhibiting the growth of several EGFR-overexpressing human tumour cell lines (e.g. colorectal (DiFi), head and neck (HN5)) both in vitro and in vivo by inducing G1 cell cycle arrest, apoptosis and terminal differentiation and 4) localizes efficiently to metastatic lesions in cancer patients (93, 118-120). By inducing antibody dependent cellular cytotoxicity (ADCC), ICR62 was also found to be very effective in the inhibiting the metastasis to the lung of cells containing EGFR mutation (i.e. EGFRvIII) in athymic mice (121) and the production of a humanised version of this antibody is currently planned (Table 4).

4.1.2. EGFR Tyrosine kinase inhibitors (TKIs)

Another class of antigen specific drugs with potential for the treatment of human cancer are the small molecule TKIs. TKIs are directed against the intracellular ATP-binding site of the EGFR tyrosine kinase domain and upon binding, they may inhibit the tyrosine phosphorylation of such receptors through reversible or irreversible mechanisms (Figure 1). EGFR TKIs have been shown to be effective in various tumour types, including lung and pancreatic cancer (122, 123). Furthermore, these agents are being extensively studied in colorectal cancer.

4.1.2.1. Gefitinib (Iressa)

Gefitinib is the first orally active, selective inhibitor of EGF that has gained approval of the US FDA for the treatment of advanced non-small cell lung cancer (122) (Table 4). Preclinical studies in colorectal cancer have demonstrated that gefitinib not only inhibited the cell growth of human colorectal tumour cells but also induced down regulation of EGFR, reduction in the basal levels of pEGFR, pMAPK, and pAKT (118). In the past decade, several clinical studies have investigated the efficacy of gefitinib against colorectal cancer (124-132). In one of the earliest phase I/II clinical studies, gefitinib in combination with oxaliplatin was evaluated in 14 patients with advanced colorectal cancer and was found to be inactive in such patients (133). In another randomised phase II trial Rothenberg et al. studied the effect of two different doses of gefitinib (250 or 500mg orally once a day) in 110 patients with recurrent colorectal adenocarcinoma. They found gefitinib to be inactive as a single agent in patients with previously treated colorectal cancers (134). Similar results were reported in several other phase I/II clinical trials (135-138). More recently, a randomised phase II study conducted by Vietez and colleagues investigated the efficacy of raltitrexed, a quinazoline antifolate inhibitor of thymidylate synthase, approved for the treatment of colorectal cancer in the EU, in combination with gefitinib as a second line therapy in 76 metastatic colorectal cancer patients. The study found no significant difference in progression free survival and overall survival (124). In contrast, two phase II studies investigated the efficacy of gefitinib in combination with 5-FU, leucovorin, and oxaliplatin in colorectal cancer patients. In the first study, of the 35 metastatic colorectal cancer patients who received treatment, complete response was seen in 40% and disease stability in 80% with a median survival time of 21.9 months (127). The second study enrolled 45 metastatic colorectal cancer patients. Based on the RECIST criteria 72% of the cases were shown to have either complete or partial response to treatment with median overall survival time of 20.5 months (126). To our knowledge, there are currently no ongoing clinical trials with gefitinib in patients with colorectal cancer.

4.1.2.2. Erlotinib (Tarceva™)

Erlotinib is a reversible inhibitor of the EGFR tyrosine kinase domain, currently approved by the US FDA for the treatment in non-small cell lung carcinoma and pancreatic cancer and is at an advance stages of clinical development in a wide range of cancers including colorectal cancer (123, 139) (Table 4) .

The role of erlotinib in colorectal cancer has been investigated in a large number of clinical studies. Unlike gefitinib, various studies have reported some clinical activity of erlotinib as a single agent (140, 141). Several other clinical studies have been conducted to evaluate erlotinib in combination with standard chemotherapy regimens in colorectal cancer. The efficacy of erlotinib in combination with capecitabine and oxaliplatin was determined in a phase II study in 32 patients who were previously treated for metastatic colorectal cancer. They observed partial response in 25% and stable disease in 44% suggesting the therapeutic potential of such combination in metastatic colorectal cancer patients who had received prior chemotherapy (142). In another phase II trial Meyerhardt and colleagues investigated the effect of erlotinib in combination with FOLFOX and the anti-VEGF mAb bevacizumab as first line therapy in 35 patients with metastatic colorectal cancer. However, due to higher level of toxicity, the study could not reach conclusions regarding the efficacy of such combination (103). In another phase I trial, Messersmith and colleagues investigated the MTD of erlotinib in combination with FOLFOX4 and bevacizumab 15 advanced colorectal adenocarcinoma patients. They found a response rate of 78% with median progression free survival of 9.5 months and median overall survival of 30 months (143). The MTD of erlotinib with FOLFOX4 with or without bevacizumab was found to be 100mg daily and despite increased toxicity it did show antitumour activity. More recently, Weickhardt and colleagues evaluated the efficacy of the dual targeting of EGFR using the combination of cetuximab and erlotinib in both preclinical and the Phase II DUX study in patients with chemo-refractory advanced colorectal cancer. Interestingly, the combination of cetuximab and erlotinib had resulted in synergistic growth inhibition of colon cancer cell lines as a result of enhanced inhibition of the EGFR pathway and differential effects on STAT3. Of 48 patients evaluated, the overall response rate was 31% with a median progression free survival of 4.6 months and mainly in patients with wild type KRAS (144). In addition, the study reported far fewer adverse effects in comparison to some of the previous studies which investigated the combination of erlotinib with standard chemotherapeutic agents (144). Several clinical trials with erlotinib in combination with anti-EGFR mAbs, bevacizumab and cytotoxic drugs are currently underway (clinicaltrials.org NCT00940316, NCT01229813, NCT01416688).

4.2. HER-2 and HER-3 targeted therapy

As noted earlier, overexpression of HER-2 and HER-3 has been reported in a variety of solid tumours including colorectal cancer (table 2 & 3). Such receptors are ideal targets for ttherapy with onoclonal antibodies, small molecule tyrosine kinase inhibitors in combination with otherapeutic interventions.

4.2.1. Trastuzumab (Herceptin)

Trastuzumab is a humanised monoclonal antibody that binds to the extracellular domain of the HER-2 receptor. Currently, it is approved for the treatment of patients with HER-2 overexpressing breast and stomach cancers (73). In colorectal cancer, a number of preclinical studies have investigated the anti-tumour activity of trastuzumab. However, very few studies have been conducted in a clinical setting with colorectal cancer patients. In one of the earliest preclinical studies, a panel of human colorectal tumour cell lines were treated with trastuzumab (mAb 4D5) and cetuximab as single agent and in combination (145). While the relative levels of HER-2, EGFR, HER-3 and HER-4 were not predictive of responsiveness to anti-HER-2 mAb 4D5, treatment with the HER-2 antibody caused a decrease in HER-2 protein levels in all of the colon cancer cell lines and also significantly decreased EGFR levels but only in the EGFR-dependent cell lines. In addition, treatment with a combination of HER-2 and EGFR antibodies caused large areas of necrosis in EGFR-dependent colon cancer xenografts supporting the superior therapeutic potential of such a combination (145). More recently in another study trastuzumab has been used in the treatment of metastatic colorectal cancer patients harbouring HER-2 gene amplification. The study found a marked radiographic response to the trastuzumab (146). However, the full therapeutic potential of trastuzumab in colorectal cancer has not yet been fully explored and warrants further investigations.

4.2.2. MM-121

Due to very weak tyrosine kinase activity, HER-3 was previously not considered as an important therapeutic target as the EGFR and HER-2. However, recent studies have demonstrated a key role of HER-3 in the activation of PI3K/AKT signalling pathway in EGFR, HER2, and the hepatocyte growth factor receptor, MET, addicted tumours and in particular resistance to HER inhibitors (90, 147-149).

MM-121 is a fully human monoclonal antibody that has entered clinical development as the first selective HER-3 antagonist (Table 4). In a recent study, MM-121 was found to effectively ligand-dependent activation of HER-3 induced by either EGFR, HER2, or MET and to abrogate resistance to anti-EGFR therapies by preventing reactivation of ErbB3 (150). These results suggest that the therapeutic potential of MM-121 in cancers with ligand-dependent activation of HER-3 (150). In another study, MM-121 was also shown to inhibit the growth in vivo of ovarian tumours (151). Currently, several clinical studies of MM-121 are underway in a range of solid tumours including colorectal cancer (clinicaltrials.gov NCT01451632).

4.3. Dual and Pan-HER Inhibitors of EGFR family members

The development of resistance to HER targeted monotherapy and the relatively small population of patients whose tumours are sensitive to treatment with a single HER blocker, as well as the co-expression of multiple members of the HER family in a varity of human cancers has stimulated research on the development of dual and pan inhibitors of HER family members and these are discussed in the following sections (Table 4).

4.3.1. Lapatinib

Lapatinib is an orally administered reversible dual receptor tyrosine kinase inhibitor of EGFR and HER-2/neu. Currently, lapatinib has been approved for the treatment of HER-2 over-expressing chemorefractory breast cancer patients (152). However, it is also under clinical investigation in other solid tumours including colorectal cancer (Table 4). Several studies have reported the therapeutic potential of lapatinib as a single agent and in combination with other chemotherapeutic agents. For example, lapatinib was found to potently inhibit the growth of a HER-2 over-expressing gastric cancer cell line and showed moderate activity in colon cancer. In addition, in combination with SN-38, the active metabolite of irinotecan, lapatinib produced synergistic growth inhibition of all human colon and gastric cancer cell lines (153). Furthermore, lapatinib was found to downregulate thymidylate synthase, which is frequently over-expressed in fluoropyrimidine resistant cancer cells, through inhibition of nuclear translocation of EGFR and HER-2 and ultimately re-sensitising such cancer cells to fluoropyrimidines (154). Most recently, a phase I/II study of lapatinib in combination with oxaliplatin and capecitabine were conducted in a small group of 12 advanced colorectal cancer patients. The full analysis is appending (clinicaltrials.gov NCT00536809).

4.3.2. Afatinib (BIBW-2992)

Currently under clinical development in solid tumours including colorectal cancer, Afatinib is an example of an irreversible pan-HER tyrosine kinase inhibitor (155) . In experimental models, afatinib was shown to be an effective and selective irreversible inhibitor of EGFR and HER-2/neu (156). In addition, afatinib was found to inhibit the total tyrosine phosphorylation of the EGFR and HER-2/neu and tumour cell proliferation in vivo (157).

More recently, we examined the effect of afatinib, as a single agent or in combination with cytotoxic drugs (5-fluorouracil, irinotecan and oxaliplatin) or anti-EGFR mAb ICR62 on the proliferation of a panel of human colorectal tumour cell lines. Afatinib inhibited the growth of EGFR-overexpressing DiFi cells (with an IC50 value of 45 nM) and other tumour cell lines with IC50 values which ranged from 0.33 �M (CCL-221) to 1.62 �M (HCT-116). There was a significant association between the co-expression of EGFR, HER-2 and HER-3 and response to treatment with afatinib (R=0.915, P=0.021) (93). In a phase II clinical trial involving 46 metastatic colorectal cancer patients afatinib produced disease-stability in 43.5% of the patients with an acceptable safety profile (158). In another recent phase I trial 53 patients received afatinib at 10 to 50mg/day. The recommended phase II dose was found to be 50mg/d and confirmed partial response was seen in 3 out of 53 patients and this was sustained for up to 34 months. A further 7/53 (13.2%) patients had disease stabilisation lasting ≥ 6 months (159). Currently, afatinib is under clinical investigation for treatment of a number of cancers including colorectal cancer (clinicaltrials.gov NCT01152437, NCT00906698)

4.3.3. HM781-36B

HM781-36B is a quinazoline-based irreversible pan-HER inhibitor and one of the latest agents to enter preclinical and clinical development for a range of human cancers. Results of the preclinical studies investigating the efficacy of HM781-36B appear to be very promising. In a recent study, the anti tumour activity of HM781-36B in combination with cytotoxic drugs was investigated in gastric cells in vitro and in vivo. HM781-36B was found to inhibit phosphorylation of all HER family members and downstream molecules accompanied with apoptosis and G1 arrest. In addition, treatment with HM781-36B in combination with chemotherapy agents was found to be superior to treatment with the single agent (160). More recently, HM781-36B was shown to be highly effective in inhibition the growth in vitro of the erlotinib resistant non-small cell lung carcinoma cells as well as other EGFR dependent cancer cells (161). Currently there are two ongoing phase I clinical studies of HM781-36B in advanced solid malignancies including colorectal cancer (clinicaltrials.gov, NCT01455584, NCT01455571).

4.3.4. Other anti-HER inhibitors

In addition to the therapeutic agents discussed above, several other mAbs and TKIs are currently at different stages of development in colorectal cancer. These agents include irreversible anti-EGFR TKIs such as EKB-569, pan TKIs such as BMS-599626 (AC480) (Table 4). For example, BMS-599626 was found to inhibit the growth of a panel of human tumour cell lines and tumour xenografts by inhibiting the formation of homodimers and heterodimers between EGFR and HER-2 (162). In another phase I trial, EKB-569 in combination with capecitabine in patients with advanced colorectal cancer, disease stability was noted in 48% of the patients (163). Furthermore, other inhibitors such as bi-specific mAb MM-111, which targets HER-2 and HER-3, is currently in phase I clinical studies for HER-2 amplified solid tumours (164)(clinicaltrials.gov, NCT00911898). These new generations of pan-HER inhibitors or bispecific antibodies should therefore have potential in the treatment of colorectal cancer patients whose tumour co-expresses different members of the HER family (Table 3 and 4). Several clinical trials are currently ongoing or have just been completed, but the results have not yet been published (clinicaltrials.gov, NCT00072748, NCT00095537).

5. PREDICTIVE MARKERS FOR RESPONSE OR RESISTANCE TO THERAPY WITH ERBB INHIBITORS IN COLORECTAL CANCER

The EGFR is an established therapeutic target in patients with colorectal cancer and the anti-EGFR mAbs cetuximab and panitumumab have been found to improve the overall survival in patients with metastatic colorectal cancer. However, many patients simply do not respond to these targeted treatments or eventually acquire resistance after a short period of time. In the following sections, we will discuss some of the predictive markers and mechanisms of resistance to EGFR targeted therapy in colorectal cancer (33, 165).

5.1. Predictive value of EGFR protein expression measured by IHC

As discussed above (section 3.1), EGFR protein expression has been reported in a large majority of studies in colorectal cancer. However, to date, there has been no clear association between EGFR protein expression and response to therapy (94, 111, 112, 166, 167). It is considered that a wide range of factors may contribute to the conflicting data on the EGFR expression and its prognostic significance in colorectal cancer, thus influencing its predictive value. Of these, the use of a particular primary antibody and various scoring systems are known to play a crucial role behind the wide variation in the EGFR protein expression and lack of correlation with response to therapy. For example, the primary antibodies (e.g. Dako PharmDx Kit) which have been routinely used in the IHC determination of EGFR and its predictive value for response to therapy with anti-EGFR inhibitors has been shown to bind both wild-type EGFR and the mutated form of this receptor (i.e. EGFRvIII) (56, 168). In addition, the majority of these studies have adopted a scoring system in which tumours with >1% of membranous staining were considered EGFR positive (i.e. nearly 100% of the cases to be EGFR positive) and hence contributing to the lack of association between EGFR expression and response to therapy (94, 166, 167, 169). Furthermore, there has been conflicting data on EGFR expression in the primary colorectal tumour and their related metastatic lesions (33, 61, 92, 169, 170)) Therefore, further studies of tumour specimens from the primary colorectal tumours and their related metastatic sites as well as tumour endothelial cells with anti-EGFR primary antibodies which are specific for the wild type EGFR and a uniform scoring system are warranted and should unravel the true potential of the EGFR protein expression as a predictive marker of response to therapy with anti-EGFR inhibitors in patients with colorectal cancer (56, 171).

5.2. Predictive value of EGFR mutations and EGFR gene amplification

Mutations of HER family members, in particular mutations in the extracellular (e.g. EGFRvIII) and intracellular (i.e. tyrosine kinase) domains of the EGFR, have been reported in a wide range of solid tumours and in some studies have been associated with response or resistance to therapy with the small molecule EGFR tyrosine kinase inhibitors. For example, treatment of non-small cell lung cancer patients containing exon 19 deletion or L858R EGFR mutations with the EGFR TKIs erlotinib and gefitinib erlotinib resulted in a significantly longer progression free survival compared to patients with wild type EGFR (p= 0.02) (172, 173) (Table 5). In contrast, a secondary mutation in the EGFR gene (T790M) was associated with acquired resistance to gefitinib and erlotinib (174). However, the mutation of the EGFR tyrosine kinase domain is rare in patients with colorectal cancer (175, 176) (Table 5). In a retrospective study of 87 archival specimens from node positive (Dukes' C) colorectal cancer patients, Cunningham and colleagues found co-expression of EGFR and EGFRvIII in 34% of the cases examined (69). Interestingly, in a more recent study, Montagut and colleagues found that an acquired mutation in the EGFR extracellular domain (S492R) prevents cetuximab binding to the human colorectal cell line DiFi and confers resistance to cetuximab. However, DiFi cells with such a mutation retained binding to and were growth inhibited by panitumumab (177). The same mutation was also detected in 2 of 10 patients with disease progression after cetuximab treatment (177). These findings suggest EGFR mutation may be a responsible factor for the development of resistance to a particular type of EGFR inhibitor, the presence of such mutations does not necessarily indicate insensitivity to other EGFR inhibitors. Therefore, current therapies for patients who develop resistance to one particular anti-EGFR therapy should still include an alternative EGFR inhibitor.

Interestingly, several studies have investigated EGFR gene amplification as a predictive biomarker for response to therapy with anti-EGFR inhibitors (53, 100, 178, 179) (Table 5). In one of the most recent studies, Algars and colleagues assessed EGFR gene copy number (GCN) from areas with the highest EGFR expression as a predictive indicator to response to anti-EGFR therapy in 80 metastatic colorectal cancer patients and found clinical benefit in 73% of high EGFR GCN patients compared to 20% of low EGFR GCN patients who showed response to therapy with cetuximab or panitumumab (180). While the findings of these studies suggest EGFR gene amplification could serve as an additional predictive marker for response to therapy with anti-EGFR inhibitors, more reliable methods of assessing EGFR gene amplification are needed and require validation in larger groups of patients.

5.3. Predictive value of EGFR ligands

In colorectal cancer, several studies have investigated the predictive value of amphiregulin and epiregulin expression in primary tumours for response to therapy with anti-EGFR mAbs in patients with colorectal cancer (Table 5). For example, Khambata et al. determined expression of epiregulin and amphiregulin in 110 metastatic colorectal cancer samples and found tumours with high expression levels of either ligands were more likely to have disease control with cetuximab (52). In another study involving 220 chemorefractory metastatic colorectal cancer patients, a significant association was found between the expression of both ligands and response to therapy with cetuximab (181). Similarly, in a more recent study Saridaki et al. also investigated expression of amphiregulin and epiregulin in 112 metastatic colorectal cancer patients and found expression of amphiregulin and epiregulin in 45% and 49% of the cases respectively. In addition, the study found significant association between the expression of epiregulin and response to cetuximab (182). Further studies involving a larger group of patients should unravel the full potential of all seven EGFR ligands as predictive biomarkers for the identification of patients who are most likely to benefit from therapy with the anti-EGFR antibodies and other EGFR inhibitors.

5.4. Predictive value of downstream cell signalling pathways

As described above, PI3K/AKT and Ras/Raf/MAPK pathways are the main signalling cascades activated by aberrant expression and activation of HER family members. In several studies, the constitutive activation of these downstream pathways by de novo mutations have been associated with acquired resistance to the EGFR inhibitors in colorectal cancer patients and some of these will be discussed in the following sections (183).

5.4.1. KRAS

KRAS is a proto-oncogene activated by EGFR signalling. Mutations within KRAS lead to a permanently activated state resulting in the activation of RAS/RAF signalling. In approximately 40% of colorectal cancer cases, KRAS is found to have a mutation (105). Many studies have found KRAS mutations to have a negative outcome on the overall survival of the patient (184, 185), whereas other studies did not find such significant associations (186) (Table 5).

In addition several studies have demonstrated KRAS mutations as a biomarker of resistance to anti-EGFR targeted therapy in colorectal cancer. In one of the first studies evaluating the clinical relevance of KRAS mutation as a marker of resistance to EGFR inhibitors; Lievre and colleagues retrospectively studied 30 patients with metastatic colorectal cancer treated with cetuximab alone or in combination with irinotecan and/or 5-fluorouracil (5-FU). The results of the study significantly associated KRAS mutations with the lack of response to cetuximab in all 11 patients (P=0.0003) (187). These initial results were reinforced by a randomised phase III study of panitumumab monotherapy versus best supportive care in 463 metastatic colorectal cancer patients. The study found KRAS mutations in 43% of the cases. While none of the patients with KRAS mutation responded to panitumumab, only 17% of patients with wild type KRAS showed response to treatment with panitumumab (188). In 2009, the US FDA approved a change for the usage of cetuximab and panitumumab to be limited to colorectal cancer patients without KRAS mutations (189). Shortly after, the results of CAIRO II phase III trials were published. The study involved 755 metastatic colorectal cancer patients who were treated with capecitabine, oxaliplatin and bevacizumab and randomised to receive cetuximab or the three drug combination. The study found the response rate to cetuximab in patients with KRAS mutations to be lower than that in patients with wild-type KRAS (46% vs 61.4% respectively) (190). However, not all patients with wild type KRAS would gain benefit from therapy with anti-EGFR mAbs. In addition, objective responses were reported in some colorectal cancer patients with KRAS mutations. For example, Stintzing and colleagues published results from the subgroup of 100 metastatic colorectal cancer patients with KRAS mutation who were treated with cetuximab and found objective response in 44% of patients (191). These studies suggest that not all tumours with KRAS mutation are resistant to therapy with anti-EGFR mAbs such as cetuximab and there is a need for the identification of more reliable predictive markers for response to the EGFR inhibitors.

5.4.2. B-RAF

Another candidate for predicting response to therapy with anti-EGFR monoclonal antibodies such cetuximab could be BRAF (Table 5). BRAF is also a member of the RAS-RAF-MAPK pathway (192). A number of studies have evaluated the prognostic value of BRAF in colorectal cancer (19, 186, 192). The predictive role for BRAF in colorectal cancer therapy was evaluated by Di Nicolantonio et al. (192). They retrospectively analysed tumour tissue from 113 patients, who had undergone previous treatment with either cetuximab or panitumumab and found 10% of the patients to have a BRAF mutation but none of them responded to therapy with anti-EGFR mAbs. In another study by Laurent-Puig and colleagues none of the 5 patients with mutated BRAF responded to treatment with cetuximab (19). There is growing evidence for the predictive value of BRAF mutation (186, 193), but these studies suffer from the small number of patients in such studies and therefore would require further validations.

5.4.3. P-I3K

HER family receptors also activate the P-I3K signalling pathway (Figure 1). Mutations in this pathway occur in around 30% of colorectal cancer patients and the majority of these occur in the exon 9 or exon 20 of PIK3CA gene which encodes the p110α isoform (194, 195). Mutant PIK3CA stimulates the AKT pathway and as a result promotes cellular growth and anti-apoptosis in a variety of human malignancies including colorectal cancer. Mutations of PIK3CA have been associated with poor response in patients with colorectal cancer in some studies (Table 5). For example, in an earlier study Sartor-Bianchi et al. investigated the association of PIK3CA mutations in 110 metastatic colorectal cancer patients with response to therapy with EGFR mAbs. The study found PIK3CA mutations in 13.6% of the cases examined and these were significantly associated with clinical resistance with panitumumab or cetuximab. Interestingly, a stronger significance between PIK3CA mutation and clinical resistance to either mAbs was observed when only KRAS wild-type patients were analysed (196). In another large study of 649 chemo-refractory metastatic colorectal cancer patients the effects of PIK3CA mutations on the efficacy of cetuximab plus chemotherapy was analysed. The study found 14.5% of the patient tumours harboured PIK3CA mutations and found a significant association between PIK3CA mutations and low response rate (197). In contrast, in another study which examined tumour specimens from 200 patients with chemo-refractory metastatic colorectal cancer found PIK3CA mutations in 12% of the cases examined and found no significant association between PIK3CA mutations and response to cetuximab. Interestingly however, the study found that patients harbouring the KRAS and PIK3CA wild-type gene responded less (30%) compared to those with PIK3CA mutations (35%) to treatment with cetuximab (198). Similarly, in another study involving 559 metastatic colorectal patients, PIK3CA mutations were found in 9.9% of the cases examined and no significant associations were found between PIK3CA mutations and response to therapy with cetuximab (55).

5.4.4. PTEN

The tumour suppressor phosphatase and tensin (PTEN) gene/protein has also been investigated in several studies as a potential predictive marker for anti-EGFR mAb response. PTEN is involved in inhibiting a PI3K initiated signalling and therefore any deregulation in the activity of PTEN could have a major impact on the progression of various cancers including colorectal cancer (199) (Table 5). Various mechanisms are responsible for the loss of activity of PTEN these include mutations, allelic losses and hypermethylation. Of these, the allelic loss of chromosome 10 is the most common cause of loss of function of PTEN in colorectal cancer (200). Several studies have investigated the loss PTEN in colorectal cancer and its association with resistance to anti-EGFR targeted therapy (19, 50, 196, 201). In a study Negri and colleagues determined PTEN status and its association to response to treatment with cetuximab in advanced colorectal cancer. The study evaluated 67 primary (n=43) and metastatic colorectal cancer (n=24) patients and found the loss of PTEN expression in the metastatic sites was negatively associated with response. Interestingly, the study also noted 25% discordance between the expression levels of PTEN in primary versus metastatic tumours (202). More recently, in another study involving 75 metastatic colorectal cancer patients, positive PTEN expression was found in 50.7% of the cases examined. The study found positive PTEN expression to be significantly associated with a favourable clinical outcome following treatment with cetuximab (203). While all these studies suggest the loss of PTEN expression is associated with clinical resistance in patients with colorectal cancer, further studies are warranted to unravel the full potential of PTEN as a predictive biomarker to response to anti-EGFR targeted therapy.

5.5. Predictive value of IGF-IR and other heterologus receptors

Another mechanism which plays a crucial role in driving resistance to anti-EGFR targeted therapy is the expression of other receptor family members such as VEGFR, PDGFR and IGF-IR and c-MET (204, 205) (Table 5) (see also Corvaia et al. and Goetschl et al., in this issue). For example, the aberrant expression of the IGF-IR has been reported in a range of human malignancies, including lung, breast, pancreas and colorectal cancer (62, 206-208). In addition, in several experimental models, IGF-IR expression has been associated with resistance to therapy with anti-EGFR and anti-HER-2 based therapies (209) (210). In one study, Cunningham and co-workers examined co-expression of IGF-IR, EGFR and HER-2 in 87 Dukes' C colorectal cancer patients using immunohistochemistry and found 93%, 83% and 89% of the cases expressed IGF-IR, EGFR, and HER-2 respectively (62). In addition, co-expression of IGF-IR, EGFR and HER-2 was common and present in 75% of the cases examined suggesting the need for further investigation of the co-targeting of such receptors using a cocktail of IGF-IR and HER inhibitors (211).

Currently, several anti-IGF-IR antibodies and small molecules IGF-IR TKIs are at different stages of clinical development in solid tumours, including patients with colorectal cancer and the results are awaited (clinicaltrials.gov, NCT01154335, NCT01016860, NCT00819169, NCT00813605, NCT00908024 (212-215) (see also Corvaia et al. in this issue) (Table 4).

While there are a limited number of studies investigating the role of IGF-IR as a potential target in colorectal cancer, the current findings appear to be very encouraging and support the inclusion of such therapies into the current therapeutic regimen for colorectal cancer patients and development of a new generation of inhibitors such as the bispecific anti-EGFR and IGF-IR antibody EI-04 (215) which could be an ideal inhibitor for use in future studies involving colorectal cancer patients with tumours co-expressing EGFR and IGF-IR (62).

6. PERSPECTIVES

It is clearly evident that the type I growth factor receptor family members and their signalling pathways play a fundamental role in tumour progression in patients with colorectal cancer. In addition, the anti-EGFR mAbs cetuximab and panitumumab have been incorporated into treatment paradigms for patients with refractory metastatic colorectal cancer. While EGFR-targeted therapies have transformed the standard care of various human cancers including colorectal cancer, only a fraction of patients will actually gain benefit from these targeted therapies and many patients simply do not respond or acquire resistance after a short period of time. In addition, there is currently no reliable predictive marker for response to therapy with HER inhibitors. In particular, there are a limited number of studies on the co-expression of all members of the HER family in patients with colorectal cancer and no studies on the expression level, prognostic significance and predictive value of all HER ligands in patients with colorectal cancer. To improve the response rate and circumvent resistance to therapy with anti-EGFR mAbs, it is considered to be essential to conduct detailed studies of the expression profiles of the various forms of the HER family members (e.g. wild type, mutated, phosphorylated), their cellular locations (e.g. nuclear, membranous, soluble) and their prognostic significance and predictive value for response to therapy with the HER inhibitors. In addition, such studies should involve the examination of both primary and metastatic lesions, as well as tumour endothelial cells on a larger group of patients. Furthermore, it is essential to determine the expression level of all the HER ligands and other receptors (e.g. IGF-IR, c-MET, PDGF-R) in patients with colorectal cancer and to determine the therapeutic benefit of anti-HER inhibitors when used in combination with agents targeting other molecular pathways and other standard therapeutic interventions. Such investigations could ultimately lead to the selection of a more specific population of colorectal cancer patients whose tumour are HER dependent and therefore are most likely to gain long term benefit from therapy with the HER inhibitors.

7. ACKNOWLEDGEMENT

This work is supported by a grant from the BRIGHT charity, UK.

8. REFERENCES

1. Ferlay, J., H. R. Shin, F. Bray, D. Forman, C. Mathers & D. M. Parkin: Estimates of worldwide burden of cancer in 2008: GLOBOCAN 2008. International Journal of Cancer2893-2917 (2010)
http://dx.doi.org/10.1002/ijc.25516
PMid:21351269

2. Center, M. M., A. Jemal, R. A. Smith & E. Ward: Worldwide Variations in Colorectal Cancer. CA Cancer J Clin, 59, 366-378 (2009)
http://dx.doi.org/10.3322/caac.20038
PMid:19897840

3. Siegel, R., D. Naishadham & A. Jemal: Cancer statistics, 2012. CA: A Cancer Journal for Clinicians, 62, 10-29 (2012)
http://dx.doi.org/10.3322/caac.20138
PMid:22237781

4. Walker, J. & P. Quirke: Prognosis and response to therapy in colorectal cancer. Eur J Cancer, 38, 880-886 (2002)
http://dx.doi.org/10.1016/S0959-8049(02)00044-8

5. Jemal, A., R. Siegel, J. Xu & E. Ward: Cancer Statistics, 2010. CA: A Cancer Journal for Clinicians, 60, 277-300 (2010)
http://dx.doi.org/10.3322/caac.20073
PMid:20610543

6. Iqbal, S. & H.-J. Lenz: Integration of novel agents in the treatment of colorectal cancer. Cancer Chemotherapy & Pharmacology, 54, S32-S39 (2004)
PMid:15309512

7. Hamilton, S. R.: Targeted therapy of cancer: new roles for pathologists in colorectal cancer. Mod Pathol, 21, S23-S30 (2008)
http://dx.doi.org/10.1038/modpathol.2008.14
PMid:18437170

8. Mason, P.: Colorectal cancer: the disease and its management. Hospital Pharmacist, 11, 175-177 (2004)

9. Wong, S.: Cetuximab: An Epidermal Growth Factor Receptor Monoclonal Antibody for the Treatment of colorectal cancer. Clinical Therapeutics, 27, 684-694 (2005)
http://dx.doi.org/10.1016/j.clinthera.2005.06.003
PMid:16117976

10. Wu, M., A. Rivkin & T. Pham: Panitumumab:Human monoclonal antibody against epidermal growth factor receptor for the treatment of metastatic colorectal cancer. Clinical Therapeutics, 30, 14-29 (2008)
http://dx.doi.org/10.1016/j.clinthera.2008.01.014
PMid:18343240

11. Shih, T. & C. Lindley: Bevacizumab: an angiogenesis inhibitor for the treatment of solid malignancies. Clinical Therapeutics, 28, 1779-802 (2006)
http://dx.doi.org/10.1016/j.clinthera.2006.11.015
PMid:17212999

12. Chu, E.: An update on the current and emerging targeted agents in metastatic colorectal cancer. Clinical Colorectal Cancer, 11, 1-13 (2012)
http://dx.doi.org/10.1016/j.clcc.2011.05.005
PMid:21752724

13. Gullick, W. G.: Prevalence of aberant expression of the epidermal growth factor receptor in human cancers. Br Med Bull, 47, 87-98 (1991)
PMid:1863851

14. Yarden, Y.: The EGFR family and its ligands in human cancer: signalling mechanisms and therapeutic opportunities. European Journal of Cancer, 37, 3-8 (2001)
http://dx.doi.org/10.1016/S0959-8049(01)00230-1

15. Lemmon, M. A. & J. Schlessinger: Cell signaling by receptor tyrosine kinases. Cell, 141, 1117-34 (2010)
http://dx.doi.org/10.1016/j.cell.2010.06.011
PMid:20602996    PMCid:2914105

16. Gullick, W.: The Type 1 growth factor receptors and their ligands considered as a complex system. Endocr Relat Cancer, 8, 75-82 (2001)
http://dx.doi.org/10.1677/erc.0.0080075
PMid:11397665

17. Singh, A. B. & R. C. Harris: Autocrine, paracrine and juxtacrine signaling by EGFR ligands. Cellular Signalling, 17, 1183-93 (2005)
http://dx.doi.org/10.1016/j.cellsig.2005.03.026
PMid:15982853

18. Burgess, A. W.: EGFR family: structure physiology signalling and therapeutic targets. Growth Factors, 26, 263-74 (2008)
http://dx.doi.org/10.1080/08977190802312844
PMid:18800267

19. Laurent-Puig, P., A. Cayre, G. Manceau, E. Buc, J.-B. Bachet, T. Lecomte, P. Rougier, A. Lievre, B. Landi, V. Boige, M. Ducreux, M. Ychou, F. Bibeau, O. Bouche, J. Reid, S. Stone & F. Penault-Llorca: Analysis of PTEN, BRAF, and EGFR Status in Determining Benefit From Cetuximab Therapy in Wild-Type KRAS Metastatic Colon Cancer. J Clin Oncol, 27, 5924-5930 (2009)
http://dx.doi.org/10.1200/JCO.2008.21.6796
PMid:19884556

20. Anklesaria, P., J. Teixidó, M. Laiho, J. H. Pierce, J. S. Greenberger & J. Massagué: Cell-cell adhesion mediated by binding of membrane-anchored transforming growth factor alpha to epidermal growth factor receptors promotes cell proliferation. Proceedings of the National Academy of Sciences of the United States of America, 87, 3289-3293 (1990)
http://dx.doi.org/10.1073/pnas.87.9.3289

21. Dent, P., D. B. Reardon, J. S. Park, G. Bowers, C. Logsdon, K. Valerie & R. Schmidt-Ullrich: Radiation-induced release of transforming growth factor alpha activates the epidermal growth factor receptor and mitogen-activated protein kinase pathway in carcinoma cells, leading to increased proliferation and protection from radiation-induced cell death. Mol Biol Cell, 10, 2493-506 (1999)
PMid:10436007    PMCid:25480

22. Giralt, J., A. Eraso, M. Armengol, J. Rossello, J. Majo, C. Ares, E. Espin, S. Benavente & I. de Torres: Epidermal growth factor receptor is a predictor of tumor response in locally advanced rectal cancer patients treated with preoperative radiotherapy. Int J Radiat Oncol Biol Phys, 54, 1460-5 (2002)
http://dx.doi.org/10.1016/S0360-3016(02)03227-3

http://dx.doi.org/10.1016/S0360-3016(02)03752-5

23. Mendelsohn, J. & J. Baselga: Status of epidermal growth factor receptor antagonists in the biology and treatment of cancer. J Clin Oncol, 21, 2787-99 (2003)
http://dx.doi.org/10.1200/JCO.2003.01.504
PMid:12860957

24. Herbst, R. S.: Review of epidermal growth factor receptor biology. Int J Radiat Oncol Biol Phys, 59, 21-6 (2004)
http://dx.doi.org/10.1016/j.ijrobp.2003.11.041
PMid:15142631

25. Hanahan, D. & R. A. Weinberg: Hallmarks of cancer: the next generation. Cell, 144, 646-74 (2011)
http://dx.doi.org/10.1016/j.cell.2011.02.013
PMid:21376230

26. Zhang, H., A. Berezov, Q. Wang, G. Zhang, J. Drebin, R. Murali & M. I. Greene: ErbB receptors: from oncogenes to targeted cancer therapies. The Journal of Clinical Investigation, 117, 2051-2058 (2007)
http://dx.doi.org/10.1172/JCI32278
PMid:17671639    PMCid:1934579

27. Modjtahedi, H. & C. Dean: The receptor for EGF and its ligands: expression, prognostic value, and target for therapy in cancer. Int J Onco, 4, 277-296 (1994)
PMid:21566922

28. Nicholson, R. I., J. W. Gee & M. E. Harper: EGFR and cancer prognosis. Eur J Cancer, 37, 9-15 (2001)
http://dx.doi.org/10.1016/S0959-8049(01)00231-3

29. Baselga, J. & C. L. Arteaga: Critical update and emerging trends in epidermal growth factor receptor targeting in cancer. Journal of Clinical Oncology, 23, 2445-59 (2005)
http://dx.doi.org/10.1200/JCO.2005.11.890
PMid:15753456

30. Zandi, R., A. B. Larsen, P. Andersen, M. T. Stockhausen & H. S. Poulsen: Mechanisms for oncogenic activation of the epidermal growth factor receptor. Cellular Signalling, 19, 2013-23 (2007)
http://dx.doi.org/10.1016/j.cellsig.2007.06.023
PMid:17681753

31. Bhola, N. E. & J. R. Grandis: Crosstalk between G-protein-coupled receptors and epidermal growth factor receptor in cancer. Frontiers in Bioscience, 13, 1857-65 (2008)
http://dx.doi.org/10.2741/2805
PMid:17981673

32. Hu, Y. P., S. B. Patil, M. Panasiewicz, W. Li, J. Hauser, L. E. Humphrey & M. G. Brattain: Heterogeneity of Receptor Function in Colon Carcinoma Cells Determined by Cross-talk between Type I Insulin-like Growth Factor Receptor and Epidermal Growth Factor Receptor. Cancer Res, 68, 8004-8013 (2008)
http://dx.doi.org/10.1158/0008-5472.CAN-08-0280
PMid:18829558

33. Modjtahedi, H. & S. Essapen: Epidermal growth factor receptor inhibitors in cancer treatment: advances, challenges and opportunities. Anticancer Drugs., 20, 851-5. (2009)
http://dx.doi.org/10.1097/CAD.0b013e3283330590
PMid:19826350

34. Lu, Y., X. Zi, Y. Zhao, D. Mascarenhas & M. Pollak: Insulin-like growth factor-I receptor signaling and resistance to trastuzumab (Herceptin). Journal of the National Cancer Institute, 93, 1852-7 (2001)
http://dx.doi.org/10.1093/jnci/93.24.1852

35. Adams, T. E., N. M. McKern & C. W. Ward: Signalling by the type 1 insulin-like growth factor receptor: interplay with the epidermal growth factor receptor. Growth Factors, 22, 89-95 (2004)
http://dx.doi.org/10.1080/08977190410001700998
PMid:15253384

36. Grossmann, A. H. & W. S. Samowitz: Epidermal Growth Factor Receptor Pathway Mutations and Colorectal Cancer Therapy. Archives of Pathology & Laboratory Medicine, 135, 1278-1282 (2011)
http://dx.doi.org/10.5858/arpa.2011-0047-RA

37. Lin, S. Y., K. Makino, W. Xia, A. Matin, Y. Wen, K. Y. Kwong, L. Bourguignon & M. C. Hung: Nuclear localization of EGF receptor and its potential new role as a transcription factor. Nature Cell Biology, 3, 802-8 (2001)
http://dx.doi.org/10.1038/ncb0901-802
PMid:11533659

http://dx.doi.org/10.1038/35078543
PMid:11389441

38. Lo, H.-W., S.-C. Hsu & M.-C. Hung: EGFR signaling pathway in breast cancers: from traditional signal transduction to direct nuclear translocalization. Breast Cancer Research & Treatment, 95, 211-218 (2006)
http://dx.doi.org/10.1007/s10549-005-9011-0
PMid:16261406

39. Dittmann, K., C. Mayer & P. H. Rodemann: Nuclear EGFR as novel therapeutic target. Strahlenther Onkologie, 186, 1-6 (2010)
http://dx.doi.org/10.1007/s00066-009-2026-4
PMid:20082181

40. Dekanic, A., R. D. Dintinjan, I. Budisavljevic, S. Pecanic, M. Z. Butorac & N. Jonjic: Strong nuclear EGFR expression in colorectal carcinomas is associated with cyclin-D1 but not with gene EGFR amplification. Diagnostic Pathology, 6, 108 (2011)
http://dx.doi.org/10.1186/1746-1596-6-108
PMid:22050898    PMCid:3225321

41. Hsu, S. C., S. A. Miller, Y. Wang & M. C. Hung: Nuclear EGFR is required for cisplatin resistance and DNA repair. American Journal of Translational Research, 1, 249-58 (2009)
PMid:19956435    PMCid:2776325

42. Hadzisejdic, I., E. Mustac, N. Jonjic, M. Petkovic & B. Grahovac: Nuclear EGFR in ductal invasive breast cancer: correlation with cyclin-D1 and prognosis. Modern Pathology, 23, 392-403 (2010)
http://dx.doi.org/10.1038/modpathol.2009.166
PMid:20062009

43. Liccardi, G., J. A. Hartley & D. Hochhauser: EGFR nuclear translocation modulates DNA repair following cisplatin and ionizing radiation treatment. Cancer Research, 71, 1103-14 (2011)
http://dx.doi.org/10.1158/0008-5472.CAN-10-2384
PMid:21266349    PMCid:3033323

44. Brand, T. M., M. Iida, C. Li & D. L. Wheeler: The nuclear epidermal growth factor receptor signaling network and its role in cancer. Discovery Medicine, 12, 419-32 (2011)
PMid:22127113    PMCid:3305885

45. Xia, W., Z. Liu, R. Zong, L. Liu, S. Zhao, S. S. Bacus, Y. Mao, J. He, J. D. Wulfkuhle, E. F. Petricoin, 3rd, T. Osada, X. Y. Yang, Z. C. Hartman, T. M. Clay, K. L. Blackwell, H. K. Lyerly & N. L. Spector: Truncated ErbB2 expressed in tumor cell nuclei contributes to acquired therapeutic resistance to ErbB2 kinase inhibitors. Molecular Cancer Therapeutics, 10, 1367-74 (2011)
http://dx.doi.org/10.1158/1535-7163.MCT-10-0991
PMid:21673090

46. Li, C., M. Iida, E. F. Dunn, A. J. Ghia & D. L. Wheeler: Nuclear EGFR contributes to acquired resistance to cetuximab. Oncogene, 28, 3801-3813 (2009)
http://dx.doi.org/10.1038/onc.2009.234
PMid:19684613    PMCid:2900381

47. Huang, W.-C., Y.-J. Chen & M.-C. Hung: Implication of nuclear EGFR in the development of resistance to anticancer therapies. Biomedicine, 1, 2-10 (2011)
http://dx.doi.org/10.1016/j.biomed.2011.10.001

48. Ooi, A., T. Takehana, X. Li, S. Suzuki, K. Kunitomo, H. Iino, H. Fujii, Y. Takeda & Y. Dobashi: Protein overexpression and gene amplification of HER-2 and EGFR in colorectal cancers: an immunohistochemical and fluorescent in situ hybridization study. Mod Pathol, 17, 895-904 (2004)
http://dx.doi.org/10.1038/modpathol.3800137
PMid:15143334

49. Spano, J.-P., C. Lagorce, D. Atlan, G. Milano, J. Domont, R. Benamouzig, A. Attar, J. Benichou, A. Martin, J.-F. Morere, M. Raphael, F. Penault-Llorca, J.-L. Breau, R. Fagard, D. Khayat & P. Wind: Impact of EGFR expression on colorectal cancer patient prognosis and survival. Ann Oncol, 16, 102-108 (2005)
http://dx.doi.org/10.1093/annonc/mdi006
PMid:15598946

50. Frattini, M., P. Saletti, E. Romagnani, V. Martin, F. Molinari, M. Ghisletta, A. Camponovo, L. L. Etienne, F. Cavalli & L. Mazzucchelli: PTEN loss of expression predicts cetuximab efficacy in metastatic colorectal cancer patients. Br J Cancer, 97, 1139-1145 (2007)
http://dx.doi.org/10.1038/sj.bjc.6604009
PMid:17940504    PMCid:2360431

51. Mayer, A., M. Takimoto, E. Fritz, G. Schellander, K. Kofler & H. Ludwig: The prognostic significance of proliferating cell nuclear antigen, epidermal growth factor receptor, and mdr gene expression in colorectal cancer. Cancer, 71, 2454-2460 (1993)
http://dx.doi.org/10.1002/1097-0142(19930415)71:8<2454::AID-CNCR2820710805>3.0.CO;2-2

52. Khambata-Ford, S., C. R. Garrett, N. J. Meropol, M. Basik, C. T. Harbison, S. Wu, T. W. Wong, X. Huang, C. H. Takimoto, A. K. Godwin, B. R. Tan, S. S. Krishnamurthi, H. A. Burris, III, E. A. Poplin, M. Hidalgo, J. Baselga, E. A. Clark & D. J. Mauro: Expression of Epiregulin and Amphiregulin and K-ras Mutation Status Predict Disease Control in Metastatic Colorectal Cancer Patients Treated With Cetuximab. J Clin Oncol, 25, 3230-3237 (2007)
http://dx.doi.org/10.1200/JCO.2006.10.5437
PMid:17664471

53. Campanella, C., M. Mottolese, A. Cianciulli, A. Torsello, R. Merola, I. Sperduti, E. Melucci, S. Conti, M. G. Diodoro, M. Zeuli, G. Paoletti, F. Cognetti & C. Garufi: Epidermal growth factor receptor gene copy number in 101 advanced colorectal cancer patients treated with chemotherapy plus cetuximab. J Transl Med, 8, 36 (2010)
http://dx.doi.org/10.1186/1479-5876-8-36
PMid:20398370    PMCid:2867799

54. Shia, J., D. S. Klimstra, A. R. Li, J. Qin, L. Saltz, J. Teruya-Feldstein, M. Akram, K. Y. Chung, D. Yao, P. B. Paty, W. Gerald & B. Chen: Epidermal growth factor receptor expression and gene amplification in colorectal carcinoma: an immunohistochemical and chromogenic in situ hybridization study. Mod Pathol, 18, 1350-1356 (2005)
http://dx.doi.org/10.1038/modpathol.3800417
PMid:15832190

55. Jolien, T., R. D. Jeroen, K. Marjolein, T. Steven, D. Martin, M. E. Vink-Börger, H. v. C. Patricia, J. H. v. Krieken, J. A. P. Cornelis & D. N. Iris: Markers for EGFR pathway activation as predictor of outcome in metastatic colorectal cancer patients treated with or without cetuximab. European journal of cancer (Oxford, England : 1990), 46, 1997-2009 (2010)

56. Modjtahedi, H., S. A. Khelwatty, R. S. Kirk, A. M. Seddon, S. Essapen, C. A. Del Vecchio, A. J. Wong & S. Eccles: Immunohistochemical discrimination of wild-type EGFR from EGFRvIII in fixed tumour specimens using anti-EGFR mAbs ICR9 and ICR10. British Journal of Cancer, 106, 883-888 (2012)
http://dx.doi.org/10.1038/bjc.2012.27
PMid:22315050    PMCid:3305949

57. Tos, A. P. D. & I. Ellis: Assessing epidermal growth factor receptor expression in tumours: What is the value of current test methods? European journal of cancer (Oxford, England : 1990), 41, 1383-1392 (2005)

58. Kluftinger, A. M., B. W. Robinson, N. F. Quenville, R. J. Finley & N. L. Davis: Correlation of epidermal growth factor receptor and c-erbB2 oncogene product to known prognostic indicators of colorectal cancer. Surgical Oncology, 1, 97-105 (1992)
http://dx.doi.org/10.1016/0960-7404(92)90062-P

59. Galizia, G., E. Lieto, F. Ferraraccio, F. De Vita, P. Castellano, M. Orditura, V. Imperatore, A. Mura, G. Manna, M. Pinto, G. Catalano, C. Pignatelli & F. Ciardiello: Prognostic Significance of Epidermal Growth Factor Receptor Expression in Colon Cancer Patients Undergoing Curative Surgery. Annals of Surgical Oncology, 13, 823-835 (2006)
http://dx.doi.org/10.1245/ASO.2006.05.052
PMid:16614884

60. Ljuslinder, I., B. Melin, M. L. Henriksson, A. Oberg & R. Palmqvist: Increased epidermal growth factor receptor expression at the invasive margin is a negative prognostic factor in colorectal cancer. International Journal of Cancer, 128, 2031-7 (2011)
http://dx.doi.org/10.1002/ijc.25559
PMid:20635387

61. Scartozzi, M., I. Bearzi, R. Berardi, A. Mandolesi, G. Fabris & S. Cascinu: Epidermal growth factor receptor (EGFR) status in primary colorectal tumors does not correlate with EGFR expression in related metastatic sites: Implications for treatment with EGFR-Targeted Monocolonal Antibodies. Journal of clinical oncology, 22, 4772-4778 (2004)
http://dx.doi.org/10.1200/JCO.2004.00.117
PMid:15570078

62. Cunningham, M. P., S. Essapen, H. Thomas, M. Green, D. P. Lovell, C. Topham, C. Marks & H. Modjtahedi: Coexpression of the IGF-IR, EGFR and HER-2 is common in colorectal cancer patients. International Journal of Oncology, 28, 329-335 (2006)
PMid:16391786

63. Takemura, K., T. Obara, S. Okano, K. Yokota, H. Ura, Y. Saitoh, Y. Koike, K. Okamura & M. Namiki: Immunohistochemical study on the expression of epidermal growth factor receptor (EGFR) in human colorectal carcinomas. Nihon Shokakibyo Gakkai Zasshi, 88, 1177-83 (1991)
PMid:1880949

64. Baiocchi, G., A. Lopes, R. Coudry, B. Rossi, F. Soares, S. Aguiar, G. Guimarães, F. Ferreira & W. Nakagawa: ErbB family immunohistochemical expression in colorectal cancer patients with higher risk of recurrence after radical surgery. International Journal of Colorectal Disease, 24, 1059-1068 (2009)
http://dx.doi.org/10.1007/s00384-009-0702-6
PMid:19390858

65. McKay, J. A., L. J. Murray, S. Curran, V. G. Ross, C. Clark, G. I. Murray, J. Cassidy & H. L. McLeod: Evaluation of the epidermal growth factor receptor (EGFR) in colorectal tumours and lymph node metastases. European Journal of Cancer, 38, 2258-2264 (2002)
http://dx.doi.org/10.1016/S0959-8049(02)00234-4

66. Yamada, M., Y. Ichikawa, S. Yamagishi, N. Momiyama, M. Ota, S. Fujii, K. Tanaka, S. Togo, S. Ohki & H. Shimada: Amphiregulin Is a Promising Prognostic Marker for Liver Metastases of Colorectal Cancer. Clinical Cancer Research, 14, 2351-2356 (2008)
http://dx.doi.org/10.1158/1078-0432.CCR-07-4499
PMid:18413824

67. Kuramochi, H., G. Nakajima, Y. Kaneko, A. Nakamura, Y. Inoue, M. Yamamoto & K. Hayashi: Amphiregulin and Epiregulin mRNA expression in primary colorectal cancer and corresponding liver metastases. BMC Cancer, 12, 88 (2012)
http://dx.doi.org/10.1186/1471-2407-12-88
PMid:22409860    PMCid:3317853

68. Baron, A. T., J. A. Wilken, D. E. Haggstrom, S. T. Goodrich & N. J. Maihle: Clinical implementation of soluble EGFR (sEGFR) as a theragnostic serum biomarker of breast, lung and ovarian cancer. IDrugs, 12, 302-8 (2009)
PMid:19431095

69. Cunningham, M. P., S. Essapen, H. Thomas, M. Green, D. P. Lovell, C. Topham, C. Marks & H. Modjtahedi: Coexpression, prognostic significance and predictive value of EGFR, EGFRvIII and phosphorylated EGFR in colorectal cancer. International Journal of Oncology, 27, 317-25 (2005)
PMid:16010411

70. Meropol, N. J.: Epidermal growth factor receptor inhibitors in colorectal cancer: it's time to get back on target. Journal of Clinical Oncology, 23, 1791-3 (2005)
http://dx.doi.org/10.1200/JCO.2005.10.951
PMid:15677698

71. Rego, R. L., N. R. Foster, T. C. Smyrk, M. Le, M. J. O'Connell, D. J. Sargent, H. Windschitl & F. A. Sinicrope: Prognostic effect of activated EGFR expression in human colon carcinomas: comparison with EGFR status. British Journal of Cancer, 102, 165-172 (2010)
http://dx.doi.org/10.1038/sj.bjc.6605473
PMid:19997103    PMCid:2813748

72. Slamon, D., G. Clark, S. Wong, W. Levin, A. Ullrich & W. McGuire: Human breast cancer: correlation of relapse and survival with amplification of the HER-2/neu oncogene. Science, 9;235, 177 - 82 (1987)
http://dx.doi.org/10.1126/science.3798106
PMid:3798106

73. Mukai, H.: Targeted Therapy in Breast Cancer: Current Status and Future Directions. Jpn. J. Clin. Oncol.hyq037 (2010)
http://dx.doi.org/10.1093/jjco/hyq037
PMid:20382634

74. Ross, J. & B. McKenna: The HER-2/neu oncogene in tumors of the gastrointestinal tract. Cancer Investigation, 19, 554-568 (2001)
http://dx.doi.org/10.1081/CNV-100103852
PMid:11458821

75. Al-Kuraya, K., H. Novotny, P. Bavi, A. K. Siraj, S. Uddin, A. Ezzat, N. A. Sanea, F. Al-Dayel, H. Al-Mana, S. S. Sheikh, M. Mirlacher, C. Tapia, R. Simon, G. Sauter, L. Terracciano & L. Tornillo: HER2, TOP2A, CCND1, EGFR and C-MYC oncogene amplification in colorectal cancer. Journal of Clinical Pathology, 60, 768-772 (2007)
http://dx.doi.org/10.1136/jcp.2006.038281
PMid:16882699    PMCid:1995777

76. Park, D., M. Kang, S. Oh, H. Kim, Y. Cho, C. Sohn, W. Jeon, B. Kim, W. Han, H. Kim, S. Ryu & A. Sepulveda: HER-2/neu overexpression is an independent prognostic factor in colorectal cancer. International Journal of Colorectal Disease, 22, 491-497 (2007)
http://dx.doi.org/10.1007/s00384-006-0192-8
PMid:16947041

77. Osako, T., M. Miyahara, S. Uchino, M. Inomata, S. Kitano & M. Kobayashi: Immunohistochemical Study of c-erbB-2 Protein in Colorectal Cancer and the Correlation with Patient Survival. Oncology, 55, 548-555 (1998)
http://dx.doi.org/10.1159/000011911
PMid:9778622

78. Kruszewski, W. J., R. Rzepko, M. Ciesielski, J. Szefel, J. Zielinski, M. Szajewski, W. Jasinski, K. Kawecki & J. Wojtacki: Expression of HER2 in colorectal cancer does not correlate with prognosis. Disease Markers, 29, 207-12 (2010)
PMid:21206005

79. Kavanagh, D., G. Chambers, L. O' Grady, K. Barry, R. Waldron, F. Bennani, P. Eustace & I. Tobbia: Is overexpression of HER-2 a predictor of prognosis in colorectal cancer? BMC Cancer, 9, 1 (2009)
http://dx.doi.org/10.1186/1471-2407-9-1
PMid:19118499    PMCid:2648993

80. Wei, Q., Y. Shui, S. Zheng, K. Wester, H. Nordgren, P. Nygren, B. Glimelius & J. Carlsson: EGFR, HER2 and HER3 expression in primary colorectal carcinomas and corresponding metastases: Implications for targeted radionuclide therapy. Oncology Reports, 25, 3-11 (2011)
PMid:21109951

81. Essapen, S., H. Thomas, M. Green, C. De Vries, M. Cook, C. Marks, C. Topham & H. Modjtahedi: The expression and prognostic significance of HER-2 in CRC. Int J Oncol, 24, 241 - 8 (2004)
PMid:14719098

82. Schuell, B., T. Gruenberger, W. Scheithauer, C. Zielinski & F. Wrba: Her-2/neu protein expression in colorectal cancer. BMC Cancer, 6, 123 (2006)
http://dx.doi.org/10.1186/1471-2407-6-123
PMid:16681853    PMCid:1475876

83. Antonacopoulou, A. G., A. C. Tsamandas, T. Petsas, A. Liava, C. D. Scopa, A. G. Papavassiliou & H. P. Kalofonos: EGFR, HER-2 and COX-2 levels in colorectal cancer. Histopathology, 53, 698-706 (2008)
http://dx.doi.org/10.1111/j.1365-2559.2008.03165.x
PMid:19102009

84. Rajkumar, T., C. S. Gooden, N. R. Lemoine, W. J. Gullick & C. S. Goden: Expression of the c-erbB-3 protein in gastrointestinal tract tumours determined by monoclonal antibody RTJ1. Journal of Pathology, 170, 271-8 (1993)
http://dx.doi.org/10.1002/path.1711700309
PMid:8133400

85. Kountourakis, P., K. Pavlakis, A. Psyrri, D. Rontogianni, N. Xiros, E. Patsouris, D. Pectasides & T. Economopoulos: Prognostic significance of HER3 and HER4 protein expression in colorectal adenocarcinomas. BMC Cancer, 6, 46 (2006)
http://dx.doi.org/10.1186/1471-2407-6-46
PMid:16507107    PMCid:1431553

86. Grivas, P. D., A. Antonacopoulou, V. Tzelepi, G. Sotiropoulou-Bonikou, Z. Kefalopoulou, A. G. Papavassiliou & H. Kalofonos: HER-3 in colorectal tumourigenesis: From mRNA levels through protein status to clinicopathologic relationships. European Journal of Cancer, 43, 2602-2611 (2007)
http://dx.doi.org/10.1016/j.ejca.2007.08.019
PMid:17920261

87. Amin, D. N., M. R. Campbell & M. M. Moasser: The role of HER3, the unpretentious member of the HER family, in cancer biology and cancer therapeutics. Seminars in Cell & Developmental Biology, 21, 944-50 (2010)
http://dx.doi.org/10.1016/j.semcdb.2010.08.007

88. Maurer, C. A., H. Friess, B. Kretschmann, A. Zimmermann, A. Stauffer, H. U. Baer, M. Korc & M. W. Buchler: Increased expression of erbB3 in colorectal cancer is associated with concomitant increase in the level of erbB2. Human Pathology, 29, 771-777 (1998)
http://dx.doi.org/10.1016/S0046-8177(98)90444-0

89. Lee, J. C., S. T. Wang, N. H. Chow & H. B. Yang: Investigation of the prognostic value of coexpressed erbB family members for the survival of colorectal cancer patients after curative surgery. European Journal of Cancer, 38, 1065-1071 (2002)
http://dx.doi.org/10.1016/S0959-8049(02)00004-7

90. Scartozzi, M., A. Mandolesi, R. Giampieri, A. Bittoni, C. Pierantoni, A. Zaniboni, E. Galizia, L. Giustini, R. R. Silva, R. Bisonni, R. Berardi, T. Biscotti, S. Biagetti, I. Bearzi & S. Cascinu: The Role of HER-3 Expression in the Prediction of Clinical Outcome for Advanced Colorectal Cancer Patients Receiving Irinotecan and Cetuximab. Oncologist, 16, 53-60 (2011)
http://dx.doi.org/10.1634/theoncologist.2010-0119
PMid:21212430    PMCid:3228051

91. Kapitanović, S., S. Rado�ević, N. Slade, M. Kapitanović, �. Anđelinović, �. Ferenčić, M. Tavassoli, �. Spaventi, K. Pavelić & R. Spaventi: Expression of erbB-3 protein in colorectal adenocarcinoma: correlation with poor survival. Journal of Cancer Research & Clinical Oncology, 126, 205-211 (2000)
http://dx.doi.org/10.1007/s004320050034

92. Ljuslinder, I., B. Malmer, M. Isaksson-Mettävainio, Å. Öberg, R. Henriksson, R. Stenling & R. Palmqvist: ErbB 1-4 expression alterations in primary colorectal cancers and their corresponding metastases. Anticancer Research, 29, 1489-1494 (2009)
PMid:19443355

93. Khelwatty, S. A., S. Essapen, A. M. Seddon & H. Modjtahedi: Growth response of human colorectal tumour cell lines to treatment with afatinib (BIBW2992), an irreversible erbB family blocker, and its association with expression of HER family members. International Journal of Oncology, 39, 483-491 (2011)
PMid:21617858

94. Cunningham, D., Y. Humblet, S. Siena, D. Khayat, H. Bleiberg, A. Santoro, D. Bets, M. Mueser, A. Harstrick, C. Verslype, I. Chau & E. Van Cutsem: Cetuximab Monotherapy and Cetuximab plus Irinotecan in Irinotecan-Refractory Metastatic Colorectal Cancer. N Engl J Med, 351, 337-345 (2004)
http://dx.doi.org/10.1056/NEJMoa033025
PMid:15269313

95. Chung, K. Y., J. Shia & N. E. Kemeny: Cetuximab shows activity in colorectal cancer patients with tumours that do not express the epidermal growth factor receptor by immunohistochemistry. J Clin Oncol, 23, 1803-10 (2005)
http://dx.doi.org/10.1200/JCO.2005.08.037
PMid:15677699

96. Lenz, H. J., E. Van Cutsem & S. Khambata-Ford: Multicenter phase II and translational study of cetuximab in metastatic colorectal carcinoma refractory to irinotecan, oxaliplatin, and fluoropyrimidines. J Clin Oncol, 24, 4914-21 (2006)
http://dx.doi.org/10.1200/JCO.2006.06.7595
PMid:17050875

97. Cappuzzo, F., M. Varella-Garcia, G. Finocchiaro, M. Skokan, S. Gajapathy, C. Carnaghi, L. Rimassa, E. Rossi, C. Ligorio, L. Di Tommaso, A. J. Holmes, L. Toschi, G. Tallini, A. Destro, M. Roncalli, A. Santoro & P. A. Janne: Primary resistance to cetuximab therapy in EGFR FISH-positive colorectal cancer patients. Br J Cancer, 99, 83-89 (2008)
http://dx.doi.org/10.1038/sj.bjc.6604439
PMid:18577988    PMCid:2453041

98. Hebbar, M., M. Ychou & M. Ducreux: Current place of high-dose irinotecan chemotherapy in patients with metastatic colorectal cancer. Journal of Cancer Research & Clinical Oncology, 135, 749-752 (2009)
http://dx.doi.org/10.1007/s00432-009-0580-x
PMid:19343364

99. Moroni, M., S. Veronese, S. Benvenuti, G. Marrapese, A. Sartore-Bianchi, F. Di Nicolantonio, M. Gambacorta, S. Siena & A. Bardelli: Gene copy number for epidermal growth factor receptor (EGFR) and clinical response to antiEGFR treatment in colorectal cancer: a cohort study. The Lancet Oncology, 6, 279-286 (2005)
http://dx.doi.org/10.1016/S1470-2045(05)70102-9

100. Sartore-Bianchi, A., M. Moroni, S. Veronese, C. Carnaghi, E. Bajetta, G. Luppi, A. Sobrero, C. Barone, S. Cascinu, G. Colucci, E. Cortesi, M. Nichelatti, M. Gambacorta & S. Siena: Epidermal Growth Factor Receptor Gene Copy Number and Clinical Outcome of Metastatic Colorectal Cancer Treated With Panitumumab. J Clin Oncol, 25, 3238-3245 (2007)
http://dx.doi.org/10.1200/JCO.2007.11.5956
PMid:17664472

101. Messersmith, W. A., D. A. Laheru, N. N. Senzer, R. C. Donehower, P. Grouleff, T. Rogers, S. K. Kelley, D. A. Ramies, B. L. Lum & M. Hidalgo: Phase I Trial of Irinotecan, Infusional 5-Fluorouracil, and Leucovorin (FOLFIRI) with Erlotinib (OSI-774). Clinical Cancer Research, 10, 6522-6527 (2004)
http://dx.doi.org/10.1158/1078-0432.CCR-04-0746

102. Townsley, C. A., P. Major, L. L. Siu, J. Dancey, E. Chen, G. R. Pond, T. Nicklee, J. Ho, D. Hedley, M. Tsao, M. J. Moore & A. M. Oza: Phase II study of erlotinib (OSI-774) in patients with metastatic colorectal cancer. Br J Cancer, 94, 1136-43 (2006)
http://dx.doi.org/10.1038/sj.bjc.6603055

103. Meyerhardt, J., K. Stuart, C. Fuchs, A. Zhu, C. Earle, P. Bhargava, L. Blaszkowsky, P. Enzinger, R. Mayer, S. Battu, C. Lawrence & D. Ryan: Phase II study of FOLFOX, bevacizumab and erlotinib as first-line therapy for patients with metastastic colorectal cancer. Ann Oncolmdm124 (2007)

104. Fan, Z., H. Masui, I. Altas & J. Mendelsohn: Blockade of epidermal growth factor receptor function by bivalent and monovalent fragments of 225 anti-epidermal growth factor receptor monoclonal antibodies. Cancer Research, 53, 4322-8 (1993)

105. Richman, S. D., M. T. Seymour, P. Chambers, F. Elliott, C. L. Daly, A. M. Meade, G. Taylor, J. H. Barrett & P. Quirke: KRAS and BRAF Mutations in Advanced Colorectal Cancer Are Associated With Poor Prognosis but Do Not Preclude Benefit From Oxaliplatin or Irinotecan: Results From the MRC FOCUS Trial. J Clin Oncol, 27, 5931-5937 (2009)
http://dx.doi.org/10.1200/JCO.2009.22.4295

106. Folprecht, G., T. Gruenberger, W. O. Bechstein, H. R. Raab, F. Lordick, J. T. Hartmann, H. Lang, A. Frilling, J. Stoehlmacher, J. Weitz, R. Konopke, C. Stroszczynski, T. Liersch, D. Ockert, T. Herrmann, E. Goekkurt, F. Parisi & C. H. Kohne: Tumour response and secondary resectability of colorectal liver metastases following neoadjuvant chemotherapy with cetuximab: the CELIM randomised phase 2 trial. Lancet Oncology, 11, 38-47 (2010)
http://dx.doi.org/10.1016/S1470-2045(09)70330-4

107. Van Cutsem, E., M. Nowacki, I. Lang, S. Cascinu, I. Shchepotin, J. Maurel, P. Rougier, D. Cunningham, J. Nippgen & C. Kohne: Randomized phase III study of irinotecan and 5-FU/FA with or without cetuximab in the first-line treatment of patients with metastatic colorectal cancer (mCRC): The CRYSTAL trial. J Clin Oncol (Meeting Abstracts), 25, 4000- (2007)

108. Sobrero, A. F., J. Maurel, L. Fehrenbacher, W. Scheithauer, Y. A. Abubakr, M. P. Lutz, M. E. Vega-Villegas, C. Eng, E. U. Steinhauer, J. Prausova, H.-J. Lenz, C. Borg, G. Middleton, H. Kroning, G. Luppi, O. Kisker, A. Zubel, C. Langer, J. Kopit & H. A. Burris, III: EPIC: Phase III Trial of Cetuximab Plus Irinotecan After Fluoropyrimidine and Oxaliplatin Failure in Patients With Metastatic Colorectal Cancer. J Clin Oncol, 26, 2311-2319 (2008)
http://dx.doi.org/10.1200/JCO.2007.13.1193

109. Keating, G. M.: Panitumumab: a review of its use in metastatic colorectal cancer. Drugs, 70, 1059-78 (2010)
http://dx.doi.org/10.2165/11205090-000000000-00000

110. Gravalos, C., J. Cassinello, P. Garcia-Alfonso & A. Jimeno: Integration of panitumumab into the treatment of colorectal cancer. Critical Reviews in Oncology/Hematology, 74, 16-26 (2010)
http://dx.doi.org/10.1016/j.critrevonc.2009.06.005

111. Van Cutsem, E., M. Peeters, S. Siena, Y. Humblet, A. Hendlisz, B. Neyns, J.-L. Canon, J.-L. Van Laethem, J. Maurel, G. Richardson, M. Wolf & R. G. Amado: Open-Label Phase III Trial of Panitumumab Plus Best Supportive Care Compared With Best Supportive Care Alone in Patients With Chemotherapy-Refractory Metastatic Colorectal Cancer. J Clin Oncol, 25, 1658-1664 (2007)
http://dx.doi.org/10.1200/JCO.2006.08.1620

112. Hecht, J. R., A. Patnaik, J. Berlin, A. Venook, I. Malik, S. Tchekmedyian, L. Navale, R. G. Amado & N. J. Meropol: Panitumumab monotherapy in patients with previously treated metastatic colorectal cancer. Cancer, 110, 980-988 (2007)
http://dx.doi.org/10.1002/cncr.22915

113. Siena, S., J. Tabernero, R. L. Burkes, J. Cassidy, D. Cunningham, M. E. Barugel, Y. Humblet, C. McPhie, M. Shing & J. Douillard: Phase III study (PRIME/20050203) of panitumumab (pmab) with FOLFOX compared with FOLFOX alone in patients (pts) with previously untreated metastatic colorectal cancer (mCRC): Pooled safety data. J Clin Oncol (Meeting Abstracts), 26, 4034- (2008)

114. Peeters, M., G. Wilson, M. Ducreux, A. Cervantes, T. Andre, Y. Hotko, F. Lordick, S. Collins, M. Shing & T. J. Price: Phase III study (20050181) of panitumumab (pmab) with FOLFIRI versus FOLFIRI alone as second-line treatment (tx) in patients (pts) with metastatic colorectal cancer (mCRC): Pooled safety results. J Clin Oncol (Meeting Abstracts), 26, 4064- (2008)

115. Li, S., P. Kussie & K. M. Ferguson: Structural basis for EGF receptor inhibition by the therapeutic antibody IMC-11F8. Structure, 16, 216-27 (2008)
http://dx.doi.org/10.1016/j.str.2007.11.009

116. Kuenen, B., P. O. Witteveen, R. Ruijter, G. Giaccone, A. Dontabhaktuni, F. Fox, T. Katz, H. Youssoufian, J. Zhu, E. K. Rowinsky & E. E. Voest: A Phase I Pharmacologic Study of Necitumumab (IMC-11F8), a Fully Human IgG1 Monoclonal Antibody Directed Against EGFR in Patients with Advanced Solid Malignancies. Clinical Cancer Research, 16, 1915-1923 (2010)
http://dx.doi.org/10.1158/1078-0432.CCR-09-2425

117. Prewett, M., J. R. Tonra, B. Rajiv, A. T. Hooper, G. Makhoul, B. Finnerty, L. Witte, P. Bohlen, Z. Zhu & D. J. Hicklin: Antitumor activity of a novel, human anti-epidermal growth factor receptor (EGFR) monoclonal antibody (IMC-11F8) in human tumor xenograft models. AACR Meeting Abstracts, 2004, 1235- (2004)

118. Cunningham, M. P., H. Thomas, Z. Fan & H. Modjtahedi: Responses of Human Colorectal Tumor Cells to Treatment with the Anti-Epidermal Growth Factor Receptor Monoclonal Antibody ICR62 Used Alone and in Combination with the EGFR Tyrosine Kinase Inhibitor Gefitinib. Cancer Research, 66, 7708-7715 (2006)
http://dx.doi.org/10.1158/0008-5472.CAN-06-1000

119. Modjtahedi, H. & C. Dean: Monoclonal antibodies to the EGF receptor act as betacellulin antagonists. Biochemical & Biophysical Research Communications, 221, 625-30 (1996)
http://dx.doi.org/10.1006/bbrc.1996.0646

120. Modjtahedi, H., S. A. Eccles, G. Box, J. Styles & C. J. Dean: Antitumor activity of combinations of antibodies directed against different epitopes on the extracellular domain of the human EGF receptor. Cell Biophysics, 22, 129-46 (1993)

121. Modjtahedi, H., D. K. Moscatello, G. Box, M. Green, C. Shoton, D. J. Lamb, L. J. Reynolds, A. J. Wong, C. Dean, H. Thomas & S. Eccles: Targeting of cells expressing wild-type EGFR and type-III mutant EGFR (EGFR VIII) by anti-EGFR MAB ICR62: A two-pronged attack for tomour therapy. Internation Journal of Cancer, 105, 273-280 (2003)
http://dx.doi.org/10.1002/ijc.11055

122. Cohen, M. H., G. A. Williams, R. Sridhara, G. Chen & R. Pazer: FDA drug approval summary: Gefitinib (ZD1839) (Iressa) tablet. Oncologist, 8, 303-306 (2003)
http://dx.doi.org/10.1634/theoncologist.8-4-303

123. Cohen, M. H., J. R. Johnson, Y.-F. Chen, R. Sridhara & R. Pazdur: FDA Drug Approval Summary: Erlotinib (Tarceva®) Tablets. The Oncologist, 10, 461-466 (2005)
http://dx.doi.org/10.1634/theoncologist.10-7-461

124. Vieitez, J. M., M. Valladares, I. Pelaez, L. de Sande Gonzalez, J. Garcia-Foncillas, J. L. Garcia-Lopez, C. Garcia-Giron, M. Reboredo, H. Bovio & A. J. Lacave: A randomized phase II study of raltitrexed and gefitinib versus raltitrexed alone as second line chemotherapy in patients with colorectal cancer. (1839IL/0143). Investigational New Drugs, 29, 1038-44 (2011)
http://dx.doi.org/10.1007/s10637-010-9400-z

125. Hartmann, J. T., J. P. Pintoffl, H. Kröning, C. Bokemeyer, M. Holtmann & T. Höhler: Gefitinib in Combination with Oxaliplatin and 5-Fluorouracil in Irinotecan-Refractory Patients with Colorectal Cancer: A Phase I Study of the Arbeits gemeinschaft Internistische Onkologie (AIO). Onkologie, 31, 237-241 (2008)
http://dx.doi.org/10.1159/000122029

126. Fisher, G. A., T. Kuo, M. Ramsey, E. Schwartz, R. V. Rouse, C. D. Cho, J. Halsey & B. I. Sikic: A phase II study of gefitinib, 5-fluorouracil, leucovorin, and oxaliplatin in previously untreated patients with metastatic colorectal cancer. Clinical Cancer Research, 14, 7074-9 (2008)
http://dx.doi.org/10.1158/1078-0432.CCR-08-1014

127. Gelibter, A. J., T. Gamucci, C. F. Pollera, F. Di Costanzo, C. Nuzzo, A. Gabriele, C. Signorelli, S. Gasperoni, V. Ferraresi, D. Giannarelli, F. Cognetti & M. Zeuli: A phase II trial of gefitinib in combination with capecitabine and oxaliplatin as first-line chemotherapy in patients with advanced colorectal cancer. Current Medical Research & Opinion, 23, 2117-23 (2007)
http://dx.doi.org/10.1185/030079907X226113

128. Meyerhardt, J. A., J. W. Clark, J. G. Supko, J. P. Eder, S. Ogino, C. F. Stewart, F. D'Amato, J. Dancey, P. C. Enzinger, A. X. Zhu, D. P. Ryan, C. C. Earle, R. J. Mayer, A. Michelini, K. Kinsella & C. S. Fuchs: Phase I study of gefitinib, irinotecan, 5-fluorouracil and leucovorin in patients with metastatic colorectal cancer. Cancer Chemotherapy & Pharmacology, 60, 661-70 (2007)
http://dx.doi.org/10.1007/s00280-006-0411-6

129. Chau, I., D. Cunningham, T. Hickish, A. Massey, L. Higgins, R. Osborne, N. Botwood & A. Swaisland: Gefitinib and irinotecan in patients with fluoropyrimidine-refractory, irinotecan-naive advanced colorectal cancer: a phase I-II study. Annals of Oncologymdl481 (2007)

130. Hofheinz, R. D., S. Kubicka, J. Wollert, D. Arnold & A. Hochhaus: Gefitinib in combination with 5-fluorouracil (5-FU)/folinic acid and irinotecan in patients with 5-FU/oxaliplatin- refractory colorectal cancer: a phase I/II study of the Arbeitsgemeinschaft fur Internistische Onkologie (AIO). Onkologie, 29, 563-7 (2006)
http://dx.doi.org/10.1159/000096449

131. Wolpin, B. M., J. W. Clark, J. A. Meyerhardt, C. C. Earle, D. P. Ryan, P. C. Enzinger, A. X. Zhu, L. Blaszkowsky, S. Battu & C. S. Fuchs: Phase I study of gefitinib plus FOLFIRI in previously untreated patients with metastatic colorectal cancer. Clinical Colorectal Cancer, 6, 208-13 (2006)
http://dx.doi.org/10.3816/CCC.2006.n.037

132. Kuo, T., C. D. Cho, J. Halsey, H. A. Wakelee, R. H. Advani, J. M. Ford, G. A. Fisher & B. I. Sikic: Phase II study of gefitinib, fluorouracil, leucovorin, and oxaliplatin therapy in previously treated patients with metastatic colorectal cancer. Journal of Clinical Oncology, 23, 5613-9 (2005)
http://dx.doi.org/10.1200/JCO.2005.08.359

133. Kindler, H. L., G. Friberg, L. Skoog, K. Wade-Oliver & E. E. Vokes: Phase I/II trial of gefitinib and oxaliplatin in patients with advanced colorectal cancer. American Journal of Clinical Oncology, 28, 340-4 (2005)
http://dx.doi.org/10.1097/01.coc.0000159558.19631.d5

134. Rothenberg, M. L., B. LaFleur, D. E. Levy, M. K. Washington, S. L. Morgan-Meadows, R. K. Ramanathan, J. D. Berlin, A. B. Benson, III & R. J. Coffey: Randomized Phase II Trial of the Clinical and Biological Effects of Two Dose Levels of Gefitinib in Patients With Recurrent Colorectal Adenocarcinoma. J Clin Oncol, 23, 9265-9274 (2005)
http://dx.doi.org/10.1200/JCO.2005.03.0536

135. Trarbach, T., A. Reinacher-Schick, S. Hegewisch-Becker, U. Vanhoefer, T. Frieling, L. Lehnert, W. Schmiegel & U. Graeven: Gefitinib in combination with capecitabine as second-line therapy in patients with advanced colorectal cancer (aCRC): a phase I/II study of the Arbeitsgemeinschaft Internistische Onkologie (AIO). Onkologie, 33, 89-93 (2010)
http://dx.doi.org/10.1159/000277635

136. Santoro, A., A. Comandone, L. Rimassa, C. Granetti, V. Lorusso, C. Oliva, M. Ronzoni, S. Siena, M. Zuradelli, E. Mari, T. Pressiani & C. Carnaghi: A phase II randomized multicenter trial of gefitinib plus FOLFIRI and FOLFIRI alone in patients with metastatic colorectal cancer. Annals of Oncology, 19, 1888-1893 (2008)
http://dx.doi.org/10.1093/annonc/mdn401

137. Jimeno, A., C. Grávalos, P. Escudero, I. Sevilla, M. Vega-Villegas, V. Alonso, I. Juez, R. García-Carbonero, H. Bovio, R. Colomer & H. Cortés-Funes: Phase I/II study of gefitinib and capecitabine in patients with colorectal cancer. Clinical & Translational Oncology, 10, 52-57 (2008)
http://dx.doi.org/10.1007/s12094-008-0153-5

138. Stebbing, J., M. Harrison, R. Glynne-Jones, J. Bridgewater & D. Propper: A phase II study to determine the ability of gefitinib to reverse fluoropyrimidine resistance in metastatic colorectal cancer (the INFORM study). British Journal of Cancer, 98, 716-9 (2008)
http://dx.doi.org/10.1038/sj.bjc.6604232

139. Kelley, R. K. & A. H. Ko: Erlotinib in the treatment of advanced pancreatic cancer. Biologics, 2, 83-95 (2008)

140. Hidalgo, M., L. L. Siu, J. Nemunaitis, J. Rizzo, L. A. Hammond, C. Takimoto, S. G. Eckhardt, A. Tolcher, C. D. Britten, L. Denis, K. Ferrante, D. D. Von Hoff, S. Silberman & E. K. Rowinsky: Phase I and Pharmacologic Study of OSI-774, an Epidermal Growth Factor Receptor Tyrosine Kinase Inhibitor, in Patients With Advanced Solid Malignancies. J Clin Oncol, 19, 3267-3279 (2001)

141. Keilholz, U., D. Arnold, N. Niederle, W. Freier, R. Porschen, T. Hoehler, F. Lordick, S. Kubicka, E. Kettner & H.-J. Schmoll: Erlotinib as 2nd and 3rd line monotherapy in patients with metastatic colorectal cancer. Results of a multicenter two-cohort phase II trial. J Clin Oncol (Meeting Abstracts), 23, 3575- (2005)

142. Meyerhardt, J. A., A. X. Zhu, P. C. Enzinger, D. P. Ryan, J. W. Clark, M. H. Kulke, C. C. Earle, M. Vincitore, A. Michelini, S. Sheehan & C. S. Fuchs: Phase II study of capecitabine, oxaliplatin, and erlotinib in previously treated patients with metastastic colorectal cancer. Journal of Clinical Oncology, 24, 1892-7 (2006)
http://dx.doi.org/10.1200/JCO.2005.05.3728

143. Messersmith, W. A., A. Jimeno, H. Jacene, M. Zhao, P. Kulesza, D. A. Laheru, Y. Kahn, A. Spira, J. Dancey, C. Iacobuzio-Donahue, R. C. Donehower, M. Carducci, M. A. Rudek & M. Hidalgo: Phase I trial of oxaliplatin, infusional 5-fluorouracil, and leucovorin (FOLFOX4) with erlotinib and bevacizumab in colorectal cancer. Clinical Colorectal Cancer, 9, 297-304 (2010)
http://dx.doi.org/10.3816/CCC.2010.n.043

144. Weickhardt, A. J., T. J. Price, G. Chong, V. Gebski, N. Pavlakis, T. G. Johns, A. Azad, E. Skrinos, K. Fluck, A. Dobrovic, R. Salemi, A. M. Scott, J. M. Mariadason & N. C. Tebbutt: Dual Targeting of the Epidermal Growth Factor Receptor Using the Combination of Cetuximab and Erlotinib: Preclinical Evaluation and Results of the Phase II DUX Study in Chemotherapy-Refractory, Advanced Colorectal Cancer. Journal of Clinical Oncology (2012)
http://dx.doi.org/10.1200/JCO.2011.38.6599

145. Kuwada, S. K., C. L. Scaife, J. Kuang, X. Li, R. F. Wong, S. R. Florell, R. J. Coffey & P. D. Gray: Effects of trastuzumab on epidermal growth factor receptor-dependent and -independent human colon cancer cells. International Journal of Cancer, 109, 291-301 (2004)
http://dx.doi.org/10.1002/ijc.11686

146. Sorscher, S. M.: Marked response to single agent trastuzumab in a patient with metastatic HER-2 gene amplified rectal cancer. Cancer Investigation, 29, 456-9 (2011)

147. Scartozzi, M., R. Giampieri, E. Maccaroni, A. Mandolesi, L. Giustini, R. Silva, A. Zaniboni, T. Biscotti, S. Biagetti, E. Galizia, F. Loupakis, A. Falcone, I. Bearzi & S. Cascinu: Analysis of HER-3, insulin growth factor-1, nuclear factor-kB and epidermal growth factor receptor gene copy number in the prediction of clinical outcome for K-RAS wild-type colorectal cancer patients receiving irinotecan-cetuximab. Annals of Oncology (2011)

148. Engelman, J. A., P. A. Janne, C. Mermel, J. Pearlberg, T. Mukohara, C. Fleet, K. Cichowski, B. E. Johnson & L. C. Cantley: ErbB-3 mediates phosphoinositide 3-kinase activity in gefitinib-sensitive non-small cell lung cancer cell lines. Proceedings of the National Academy of Sciences of the United States of America, 102, 3788-93 (2005)
http://dx.doi.org/10.1073/pnas.0409773102

149. Engelman, J. A., K. Zejnullahu, T. Mitsudomi, Y. Song, C. Hyland, J. O. Park, N. Lindeman, C. M. Gale, X. Zhao, J. Christensen, T. Kosaka, A. J. Holmes, A. M. Rogers, F. Cappuzzo, T. Mok, C. Lee, B. E. Johnson, L. C. Cantley & P. A. Janne: MET amplification leads to gefitinib resistance in lung cancer by activating ERBB3 signaling. Science, 316, 1039-43 (2007)
http://dx.doi.org/10.1126/science.1141478

150. Schoeberl, B., E. A. Pace, J. B. Fitzgerald, B. D. Harms, L. Xu, L. Nie, B. Linggi, A. Kalra, V. Paragas, R. Bukhalid, V. Grantcharova, N. Kohli, K. A. West, M. Leszczyniecka, M. J. Feldhaus, A. J. Kudla & U. B. Nielsen: Therapeutically Targeting ErbB3: A Key Node in Ligand-Induced Activation of the ErbB Receptor-PI3K Axis. Sci. Signal., 2, ra31- (2009)

151. Sheng, Q., X. Liu, E. Fleming, K. Yuan, H. Piao, J. Chen, Z. Moustafa, R. K. Thomas, H. Greulich, A. Schinzel, S. Zaghlul, D. Batt, S. Ettenberg, M. Meyerson, B. Schoeberl, A. L. Kung, W. C. Hahn, R. Drapkin, D. M. Livingston & J. F. Liu: An Activated ErbB3/NRG1 Autocrine Loop Supports In vivo Proliferation in Ovarian Cancer Cells. Cancer Cell, 17, 298-310 (2010)
http://dx.doi.org/10.1016/j.ccr.2009.12.047
PMid:20227043    PMCid:2897158

152. Geyer, C. E., J. Forster, D. Lindquist, S. Chan, C. G. Romieu, T. Pienkowski, A. Jagiello-Gruszfeld, J. Crown, A. Chan, B. Kaufman, D. Skarlos, M. Campone, N. Davidson, M. Berger, C. Oliva, S. D. Rubin, S. Stein & D. Cameron: Lapatinib plus Capecitabine for HER2-Positive Advanced Breast Cancer. N Engl J Med, 355, 2733-2743 (2006)
http://dx.doi.org/10.1056/NEJMoa064320
PMid:17192538

153. LaBonte, M. J., P. C. Manegold, P. M. Wilson, W. Fazzone, S. G. Louie, H.-J. Lenz & R. D. Ladner: The dual EGFR/HER-2 tyrosine kinase inhibitor lapatinib sensitizes colon and gastric cancer cells to the irinotecan active metabolite SN-38. International Journal of Cancer, 125, 2957-2969 (2009)
http://dx.doi.org/10.1002/ijc.24658
PMid:19536776

154. Kim, H. P., Y. K. Yoon, J. W. Kim, S. W. Han, H. S. Hur, J. Park, J. H. Lee, D. Y. Oh, S. A. Im, Y. J. Bang & T. Y. Kim: Lapatinib, a dual EGFR and HER2 tyrosine kinase inhibitor, downregulates thymidylate synthase by inhibiting the nuclear translocation of EGFR and HER2. PLoS ONE, 4, e5933 (2009)
http://dx.doi.org/10.1371/journal.pone.0005933
PMid:19529774    PMCid:2691960

155. Solca, F.: Pharmacology and molecular mechanisms of BIBW2992 a potent irreversible dual EGFR/HER-2 kinase inhibitor of cancer therapy. Targeted Oncology, 2, S15 (2007)

156. Eskens, F. A. L. M., C. H. Mom, A. S. T. Planting, J. A. Gietema, A. Amelsberg, H. Huisman, L. van Doorn, H. Burger, P. Stopfer, J. Verweij & E. G. E. de Vries: A phase I dose escalation study of BIBW 2992, an irreversible dual inhibitor of epidermal growth factor receptor 1 (EGFR) and 2 (HER2) tyrosine kinase in a 2-week on, 2-week off schedule in patients with advanced solid tumours. British Journal of Cancer, 98, 80-85 (2007)
http://dx.doi.org/10.1038/sj.bjc.6604108
PMid:18026190    PMCid:2359721

157. Minkovsky, N. & A. Berezov: BIBW-2992, a dual receptor tyrosine kinase inhibitor for the treatment of solid tumors. Curr Opin Investig Drugs, 9, 1336-46 (2008)
PMid:19037840

158. Bouche, O., M. Ducreux, G. Lledo, T. Andre, F. Maindrault-Goebel, P. Stopfer, Z. Oum'Hamed, M. Chadjaa & A. de Gramont: A Phase II Trial of Weekly Alternating Sequential Administration of BIBF 1120 and BIBW 2992 in Patients With Advanced Colorectal Cancer. J Clin Oncol, 26, (2008)
PMid:18165637

159. Yap, T. A., L. Vidal, J. Adam, P. Stephens, J. Spicer, H. Shaw, J. Ang, G. Temple, S. Bell, M. Shahidi, M. Uttenreuther-Fischer, P. Stopfer, A. Futreal, H. Calvert, J. S. de Bono & R. Plummer: Phase I Trial of the Irreversible EGFR and HER2 Kinase Inhibitor BIBW 2992 in Patients With Advanced Solid Tumors. J Clin Oncol, 28, 3965-3972 (2010)
http://dx.doi.org/10.1200/JCO.2009.26.7278
PMid:20679611

160. Nam, H.-J., H.-P. Kim, Y.-K. Yoon, H.-S. Hur, S.-H. Song, M.-S. Kim, G.-S. Lee, S.-W. Han, S.-A. Im & T.-Y. Kim: Antitumor activity of HM781-36B, an irreversible Pan-HER inhibitor, alone or in combination with cytotoxic chemotherapeutic agents in gastric cancer. Cancer Letters, 302, 155-165 (2011)
http://dx.doi.org/10.1016/j.canlet.2011.01.010
PMid:21306821

161. Cha, M. Y., K. O. Lee, M. Kim, J. Y. Song, K. H. Lee, J. Park, Y. J. Chae, Y. H. Kim, K. H. Suh, G. S. Lee, S. B. Park & M. S. Kim: Antitumor activity of HM781-36B, a highly effective pan-HER inhibitor in erlotinib-resistant NSCLC and other EGFR-dependent cancer models. International Journal of Cancer, 130, 2445-54 (2012)
http://dx.doi.org/10.1002/ijc.26276
PMid:21732342

162. Wong, T. W., F. Y. Lee, C. Yu, F. R. Luo, S. Oppenheimer, H. Zhang, R. A. Smykla, H. Mastalerz, B. E. Fink, J. T. Hunt, A. V. Gavai & G. D. Vite: Preclinical antitumor activity of BMS-599626, a pan-HER kinase inhibitor that inhibits HER1/HER2 homodimer and heterodimer signaling. Clinical Cancer Research, 12, 6186-93 (2006)
http://dx.doi.org/10.1158/1078-0432.CCR-06-0642
PMid:17062696

163. Laheru, D., G. Croghan, R. Bukowski, M. Rudek, W. Messersmith, C. Erlichman, R. Pelley, A. Jimeno, R. Donehower, J. Boni, R. Abbas, P. Martins, C. Zacharchuk & M. Hidalgo: A phase I study of EKB-569 in combination with capecitabine in patients with advanced colorectal cancer. Clinical Cancer Research, 14, 5602-9 (2008)
http://dx.doi.org/10.1158/1078-0432.CCR-08-0433
PMid:18765554    PMCid:3086427

164. McDonagh, C. F., A. Huhalov, B. D. Harms, S. Adams, V. Paragas, S. Oyama, B. Zhang, L. Luus, R. Overland, S. Nguyen, J. Gu, N. Kohli, M. Wallace, M. J. Feldhaus, A. J. Kudla, B. Schoeberl & U. B. Nielsen: Antitumor Activity of a Novel Bispecific Antibody That Targets the ErbB2/ErbB3 Oncogenic Unit and Inhibits Heregulin-Induced Activation of ErbB3. Molecular Cancer Therapeutics, 11, 582-93 (2012)
http://dx.doi.org/10.1158/1535-7163.MCT-11-0820
PMid:22248472

165. Siena, S., A. Sartore-Bianchi, F. Di Nicolantonio, J. Balfour & A. Bardelli: Biomarkers predicting clinical outcome of epidermal growth factor receptor-targeted therapy in metastatic colorectal cancer. Journal of the National Cancer Institute, 101, 1308-24 (2009)
http://dx.doi.org/10.1093/jnci/djp280
PMid:19738166    PMCid:2758310

166. Saltz, L. B., N. J. Meropol, P. J. Loehrer, Sr, M. N. Needle, J. Kopit & R. J. Mayer: Phase II Trial of Cetuximab in Patients With Refractory Colorectal Cancer That Expresses the Epidermal Growth Factor Receptor. J Clin Oncol, 22, 1201-1208 (2004)
http://dx.doi.org/10.1200/JCO.2004.10.182
PMid:14993230

167. Hecht, J. R., E. Mitchell, M. A. Neubauer, H. A. Burris Iii, P. Swanson, T. Lopez, G. Buchanan, M. Reiner, J. Gansert & J. Berlin: Lack of correlation between epidermal growth factor receptor status and response to panitumumab monotherapy in metastatic colorectal cancer. Clinical Cancer Research, 16, 2205-2213 (2010)
http://dx.doi.org/10.1158/1078-0432.CCR-09-2017
PMid:20332321

168. Han, H.-S., H. J. Chang, Y. S. Hong, S. Y. Kim, K. S. Lee & K. H. Jung: Epidermal Growth Factor Receptor Expression Discrepancies in Metastatic Colorectal Cancer Patients Treated with Cetuximab Plus Irinotecan-Based Chemotherapy Refractory to Irinotecan and Oxaliplatin. Diseases of the Colon & Rectum, 52, 1144-1151 (2009)
http://dx.doi.org/10.1007/DCR.0b013e31819edbf9

169. Yarom, N., C. Marginean, T. Moyana, I. Gorn-Hondermann, H. C. Birnboim, H. Marginean, R. C. Auer, M. Vickers, T. R. Asmis, J. Maroun & D. Jonker: EGFR expression variance in paired colorectal cancer primary and metastatic tumors. Cancer Biology & Therapy, 10, 416-421 (2010)
http://dx.doi.org/10.4161/cbt.10.5.12610

170. Bralet, M. P., B. Paule, B. Falissard, R. Adam & C. Guettier: Immunohistochemical variability of epidermal growth factor receptor (EGFR) in liver metastases from clonic carcinomas. Histopathology, 50, 210-216 (2007)
http://dx.doi.org/10.1111/j.1365-2559.2007.02578.x
PMid:17222249

171. Amin, D. N., K. Hida, D. R. Bielenberg & M. Klagsbrun: Tumor endothelial cells express epidermal growth factor receptor (EGFR) but not ErbB3 and are responsive to EGF and to EGFR kinase inhibitors. Cancer Research, 66, 2173-80 (2006)
http://dx.doi.org/10.1158/0008-5472.CAN-05-3387
PMid:16489018

172. Won, Y.-W., J.-Y. Han, G. K. Lee, S.-Y. Park, K. Y. Lim, K.-A. Yoon, T. Yun, H. T. Kim & J. S. Lee: Comparison of clinical outcome of patients with non-small-cell lung cancer harbouring epidermal growth factor receptor exon 19 or exon 21 mutations. Journal of Clinical Pathology, 64, 947-952 (2011)
http://dx.doi.org/10.1136/jclinpath-2011-200169
PMid:21725039

173. Martínez-Navarro, E., J. Rebollo, R. González-Manzano, M. Sureda, E. Evgenyeva, B. Valenzuela, F. Fernández, J. Forteza & A. Brugarolas: Epidermal growth factor receptor (EGFR) mutations in a series of non-small-cell lung cancer (NSCLC) patients and response rate to EGFR-specific tyrosine kinase inhibitors (TKIs). Clinical & Translational Oncology, 13, 812-818 (2011)
http://dx.doi.org/10.1007/s12094-011-0739-1

174. Ma, C., S. Wei & Y. Song: T790M and acquired resistance of EGFR TKI: a literature review of clinical reports. J Thorac Dis, 3, 10-8 (2011)
PMid:22263058    PMCid:3256494

175. Lee, J. W., Y. H. Soung, S. Y. Kim, W. S. Park, S. W. Nam, J. Y. Lee, N. J. Yoo & S. H. Lee: Absence of EGFR mutation in the kinase domain in common human cancers besides non-small cell lung cancer. International Journal of Cancer, 113, 510-1 (2005)
http://dx.doi.org/10.1002/ijc.20591
PMid:15455340

176. Barber, T. D., B. Vogelstein, K. W. Kinzler & V. E. Velculescu: Somatic mutations of EGFR in colorectal cancers and glioblastomas. New England Journal of Medicine, 351, 2883 (2004)
http://dx.doi.org/10.1056/NEJM200412303512724
PMid:15625347

177. Montagut, C., A. Dalmases, B. Bellosillo, M. Crespo, S. Pairet, M. Iglesias, M. Salido, M. Gallen, S. Marsters, S. P. Tsai, A. Minoche, S. Somasekar, S. Serrano, H. Himmelbauer, J. Bellmunt, A. Rovira, J. Settleman, F. Bosch & J. Albanell: Identification of a mutation in the extracellular domain of the Epidermal Growth Factor Receptor conferring cetuximab resistance in colorectal cancer. Nature Medicine, 18, 221-3 (2012)
http://dx.doi.org/10.1038/nm.2609
PMid:22270724

178. Cappuzzo, F., G. Finocchiaro, E. Rossi, P. A. Janne, C. Carnaghi, C. Calandri, K. Bencardino, C. Ligorio, F. Ciardiello, T. Pressiani, A. Destro, M. Roncalli, L. Crino, W. A. Franklin, A. Santoro & M. Varella-Garcia: EGFR FISH assay predicts for response to cetuximab in chemotherapy refractory colorectal cancer patients. Annals of Oncology, 19, 717-23 (2008)
http://dx.doi.org/10.1093/annonc/mdm492
PMid:17974556

179. Personeni, N., S. Fieuws, H. Piessevaux, G. De Hertogh, J. De Schutter, B. Biesmans, W. De Roock, A. Capoen, M. Debiec-Rychter, J. L. Van Laethem, M. Peeters, Y. Humblet, E. Van Cutsem & S. Tejpar: Clinical usefulness of EGFR gene copy number as a predictive marker in colorectal cancer patients treated with cetuximab: a fluorescent in situ hybridization study. Clinical Cancer Research, 14, 5869-76 (2008)
http://dx.doi.org/10.1158/1078-0432.CCR-08-0449
PMid:18794099

180. Algars, A., M. Lintunen, O. Carpen, R. Ristamaki & J. Sundstrom: EGFR gene copy number assessment from areas with highest EGFR expression predicts response to anti-EGFR therapy in colorectal cancer. British Journal of Cancer, 105, 255-262 (2011)
http://dx.doi.org/10.1038/bjc.2011.223
PMid:21694725    PMCid:3142805

181. Jacobs, B., W. De Roock, H. Piessevaux, R. Van Oirbeek, B. Biesmans, J. De Schutter, S. Fieuws, J. Vandesompele, M. Peeters, J. L. Van Laethem, Y. Humblet, F. Penault-Llorca, G. De Hertogh, P. Laurent-Puig, E. Van Cutsem & S. Tejpar: Amphiregulin and epiregulin mRNA expression in primary tumors predicts outcome in metastatic colorectal cancer treated with cetuximab. Journal of Clinical Oncology, 27, 5068-74 (2009)
http://dx.doi.org/10.1200/JCO.2008.21.3744
PMid:19738126

182. Saridaki, Z., M. Tzardi, C. Papadaki, M. Sfakianaki, F. Pega, A. Kalikaki, E. Tsakalaki, M. Trypaki, I. Messaritakis, E. Stathopoulos, D. Mavroudis, V. Georgoulias & J. Souglakos: Impact of KRAS, BRAF, PIK3CA mutations, PTEN, AREG, EREG expression and skin rash in 2 line cetuximab-based therapy of colorectal cancer patients. PLoS ONE, 6, e15980 (2011)
http://dx.doi.org/10.1371/journal.pone.0015980
PMid:21283802    PMCid:3024325

183. Di Fiore, F., R. Sesboue, P. Michel, J. C. Sabourin & T. Frebourg: Molecular determinants of anti-EGFR sensitivity and resistance in metastatic colorectal cancer. Br J Cancer, 103, 1765-1772 (2010)
http://dx.doi.org/10.1038/sj.bjc.6606008
PMid:21139621    PMCid:3008616

184. Lievre, A., J.-B. Bachet, V. Boige, A. Cayre, D. Le Corre, E. Buc, M. Ychou, O. Bouche, B. Landi, C. Louvet, T. Andre, F. Bibeau, M.-D. Diebold, P. Rougier, M. Ducreux, G. Tomasic, J.-F. Emile, F. Penault-Llorca & P. Laurent-Puig: KRAS Mutations As an Independent Prognostic Factor in Patients With Advanced Colorectal Cancer Treated With Cetuximab. J Clin Oncol, 26, 374-379 (2008)
http://dx.doi.org/10.1200/JCO.2007.12.5906
PMid:18202412

185. Yen, L. C., Y. H. Uen, D. C. Wu, C. Y. Lu, F. J. Yu, I. C. Wu, S. R. Lin & J. Y. Wang: Activating KRAS Mutations and Overexpression of Epidermal Growth Factor Receptor as Independent Predictors in Metastatic Colorectal Cancer Patients Treated With Cetuximab. Annals of Surgery, 251, 254-260 (2010)
http://dx.doi.org/10.1097/SLA.0b013e3181bc9d96
PMid:20010090

186. Roth, A. D., S. Tejpar, M. Delorenzi, P. Yan, R. Fiocca, D. Klingbiel, D. Dietrich, B. Biesmans, G. Bodoky, C. Barone, E. Aranda, B. Nordlinger, L. Cisar, R. Labianca, D. Cunningham, E. Van Cutsem & F. Bosman: Prognostic Role of KRAS and BRAF in Stage II and III Resected Colon Cancer: Results of the Translational Study on the PETACC-3, EORTC 40993, SAKK 60-00 Trial. J Clin Oncol, 28, 466-474 (2010)
http://dx.doi.org/10.1200/JCO.2009.23.3452
PMid:20008640

187. Lievre, A., J.-B. Bachet, D. Le Corre, V. Boige, B. Landi, J.-F. Emile, J.-F. Cote, G. Tomasic, C. Penna, M. Ducreux, P. Rougier, F. Penault-Llorca & P. Laurent-Puig: KRAS Mutation Status Is Predictive of Response to Cetuximab Therapy in Colorectal Cancer. Cancer Res, 66, 3992-3995 (2006)
http://dx.doi.org/10.1158/0008-5472.CAN-06-0191
PMid:16618717

188. Amado, R. G., M. Wolf, M. Peeters, E. Van Cutsem, S. Siena, D. J. Freeman, T. Juan, R. Sikorski, S. Suggs, R. Radinsky, S. D. Patterson & D. D. Chang: Wild-Type KRAS Is Required for Panitumumab Efficacy in Patients With Metastatic Colorectal Cancer. J Clin Oncol, 26, 1626-1634 (2008)
http://dx.doi.org/10.1200/JCO.2007.14.7116
PMid:18316791

189. Allegra, C. J., J. M. Jessup, M. R. Somerfield, S. R. Hamilton, E. H. Hammond, D. F. Hayes, P. K. McAllister, R. F. Morton & R. L. Schilsky: American Society of Clinical Oncology Provisional Clinical Opinion: Testing for KRAS Gene Mutations in Patients With Metastatic Colorectal Carcinoma to Predict Response to Anti-Epidermal Growth Factor Receptor Monoclonal Antibody Therapy. J Clin Oncol, 27, 2091-2096 (2009)
http://dx.doi.org/10.1200/JCO.2009.21.9170
PMid:19188670

190. Tol, J., M. Koopman, A. Cats, C. J. Rodenburg, G. J. Creemers, J. G. Schrama, F. L. Erdkamp, A. H. Vos, C. J. van Groeningen, H. A. Sinnige, D. J. Richel, E. E. Voest, J. R. Dijkstra, M. E. Vink-Borger, N. F. Antonini, L. Mol, J. H. van Krieken, O. Dalesio & C. J. Punt: Chemotherapy, bevacizumab, and cetuximab in metastatic colorectal cancer. New England Journal of Medicine, 360, 563-72 (2009)
http://dx.doi.org/10.1056/NEJMoa0808268
PMid:19196673

191. Stintzing, S., L. Fischer von Weikersthal, T. Decker, U. Vehling-Kaiser, E. Jager, T. Heintges, C. Stoll, C. Giessen, D. P. Modest, J. Neumann, A. Jung, T. Kirchner, W. Scheithauer & V. Heinemann: FOLFIRI plus cetuximab versus FOLFIRI plus bevacizumab as first-line treatment for patients with metastatic colorectal cancer-subgroup analysis of patients with KRAS: mutated tumours in the randomised German AIO study KRK-0306. Annals of Oncology (2012)
http://dx.doi.org/10.1093/annonc/mdr571
PMid:22219013

192. Di Nicolantonio, F., M. Martini, F. Molinari, A. Sartore-Bianchi, S. Arena, P. Saletti, S. De Dosso, L. Mazzucchelli, M. Frattini, S. Siena & A. Bardelli: Wild-Type BRAF Is Required for Response to Panitumumab or Cetuximab in Metastatic Colorectal Cancer. J Clin Oncol, 26, 5705-5712 (2008)
http://dx.doi.org/10.1200/JCO.2008.18.0786
PMid:19001320

193. Yokota, T.: Are KRAS/BRAF mutations potent prognostic and/or predictive biomarkers in colorectal cancers? Anti-Cancer Agents in Medicinal Chemistry, 12, 163-71 (2012)
PMid:22043994    PMCid:3343383

194. Nosho, K., T. Kawasaki, M. Ohnishi, Y. Suemoto, G. J. Kirkner, D. Zepf, L. Yan, J. A. Longtine, C. S. Fuchs & S. Ogino: PIK3CA mutation in colorectal cancer: relationship with genetic and epigenetic alterations. Neoplasia, 10, 534-41 (2008)
PMid:18516290    PMCid:2386538

195. Barault, L., N. Veyrie, V. Jooste, D. Lecorre, C. Chapusot, J. M. Ferraz, A. Lievre, M. Cortet, A. M. Bouvier, P. Rat, P. Roignot, J. Faivre, P. Laurent-Puig & F. Piard: Mutations in the RAS-MAPK, PI(3)K (phosphatidylinositol-3-OH kinase) signaling network correlate with poor survival in a population-based series of colon cancers. International Journal of Cancer, 122, 2255-9 (2008)
http://dx.doi.org/10.1002/ijc.23388
PMid:18224685

196. Sartore-Bianchi, A., M. Martini, F. Molinari, S. Veronese, M. Nichelatti, S. Artale, F. Di Nicolantonio, P. Saletti, S. De Dosso, L. Mazzucchelli, M. Frattini, S. Siena & A. Bardelli: PIK3CA mutations in colorectal cancer are associated with clinical resistance to EGFR-targeted monoclonal antibodies. Cancer Research, 69, 1851-7 (2009)
http://dx.doi.org/10.1158/0008-5472.CAN-08-2466
PMid:19223544

197. De Roock, W., B. Claes, D. Bernasconi, J. De Schutter, B. Biesmans, G. Fountzilas, K. T. Kalogeras, V. Kotoula, D. Papamichael, P. Laurent-Puig, F. Penault-Llorca, P. Rougier, B. Vincenzi, D. Santini, G. Tonini, F. Cappuzzo, M. Frattini, F. Molinari, P. Saletti, S. De Dosso, M. Martini, A. Bardelli, S. Siena, A. Sartore-Bianchi, J. Tabernero, T. Macarulla, F. Di Fiore, A. O. Gangloff, F. Ciardiello, P. Pfeiffer, C. Qvortrup, T. P. Hansen, E. Van Cutsem, H. Piessevaux, D. Lambrechts, M. Delorenzi & S. Tejpar: Effects of KRAS, BRAF, NRAS, and PIK3CAmutations on the efficacy of cetuximab plus chemotherapy in chemotherapy-refractory metastatic colorectal cancer: a retrospective consortium analysis. The Lancet Oncology, 11, 753-762 (2010)
http://dx.doi.org/10.1016/S1470-2045(10)70130-3

198. Prenen, H., J. De Schutter, B. Jacobs, W. De Roock, B. Biesmans, B. Claes, D. Lambrechts, E. Van Cutsem & S. Tejpar: PIK3CA mutations are not a major determinant of resistance to the epidermal growth factor receptor inhibitor cetuximab in metastatic colorectal cancer. Clinical Cancer Research, 15, 3184-8 (2009)
http://dx.doi.org/10.1158/1078-0432.CCR-08-2961
PMid:19366826

199. Nagata, Y., K. H. Lan, X. Zhou, M. Tan, F. J. Esteva, A. A. Sahin, K. S. Klos, P. Li, B. P. Monia, N. T. Nguyen, G. N. Hortobagyi, M. C. Hung & D. Yu: PTEN activation contributes to tumor inhibition by trastuzumab, and loss of PTEN predicts trastuzumab resistance in patients. Cancer Cell, 6, 117-27 (2004)
http://dx.doi.org/10.1016/j.ccr.2004.06.022
PMid:15324695

200. Stambolic, V., A. Suzuki, J. L. de la Pompa, G. M. Brothers, C. Mirtsos, T. Sasaki, J. Ruland, J. M. Penninger, D. P. Siderovski & T. W. Mak: Negative regulation of PKB/Akt-dependent cell survival by the tumor suppressor PTEN. Cell, 95, 29-39 (1998)
http://dx.doi.org/10.1016/S0092-8674(00)81780-8

201. Loupakis, F., L. Pollina, I. Stasi, A. Ruzzo, M. Scartozzi, D. Santini, G. Masi, F. Graziano, C. Cremolini, E. Rulli, E. Canestrari, N. Funel, G. Schiavon, I. Petrini, M. Magnani, G. Tonini, D. Campani, I. Floriani, S. Cascinu & A. Falcone: PTEN expression and KRAS mutations on primary tumors and metastases in the prediction of benefit from cetuximab plus irinotecan for patients with metastatic colorectal cancer. Journal of Clinical Oncology, 27, 2622-9 (2009)
http://dx.doi.org/10.1200/JCO.2008.20.2796
PMid:19398573

202. Negri, F. V., C. Bozzetti, C. A. Lagrasta, P. Crafa, M. P. Bonasoni, R. Camisa, G. Pedrazzi & A. Ardizzoni: PTEN status in advanced colorectal cancer treated with cetuximab. British Journal of Cancer, 102, 162-164 (2010)
http://dx.doi.org/10.1038/sj.bjc.6605471
PMid:19953097    PMCid:2813733

203. Park, J. H., S. W. Han, D. Y. Oh, S. A. Im, S. Y. Jeong, K. J. Park, T. Y. Kim, Y. J. Bang & J. G. Park: Analysis of KRAS, BRAF, PTEN, IGF1R, EGFR intron 1 CA status in both primary tumors and paired metastases in determining benefit from cetuximab therapy in colon cancer. Cancer Chemotherapy & Pharmacology1-11 (2011)

204. Dewaele, B., G. Floris, J. Finalet-Ferreiro, C. D. Fletcher, J. M. Coindre, L. Guillou, P. C. Hogendoorn, A. Wozniak, V. Vanspauwen, P. Schoffski, P. Marynen, P. Vandenberghe, R. Sciot & M. Debiec-Rychter: Coactivated platelet-derived growth factor receptor {alpha, #1280} and epidermal growth factor receptor are potential therapeutic targets in intimal sarcoma. Cancer Research, 70, 7304-14 (2010)
http://dx.doi.org/10.1158/0008-5472.CAN-10-1543
PMid:20685895

205. Krumbach, R., J. Schuler, M. Hofmann, T. Giesemann, H. H. Fiebig & T. Beckers: Primary resistance to cetuximab in a panel of patient-derived tumour xenograft models: activation of MET as one mechanism for drug resistance. European Journal of Cancer, 47, 1231-43 (2011)
http://dx.doi.org/10.1016/j.ejca.2010.12.019
PMid:21273060

206. Peters, G., S. Gongoll, C. Langner, M. Mengel, P. Piso, J. Klempnauer, J. Rüschoff, H. Kreipe & R. von Wasielewski: IGF-1R, IGF-1 and IGF-2 expression as potential prognostic and predictive markers in colorectal-cancer. Virchows Archiv, 443, 139-145 (2003)
http://dx.doi.org/10.1007/s00428-003-0856-5
PMid:12845531

207. Weber, M. M., C. Fottner, S. B. Liu, M. C. Jung, D. Engelhardt & G. B. Baretton: Overexpression of the insulin-like growth factor I receptor in human colon carcinomas. Cancer, 95, 2086-2095 (2002)
http://dx.doi.org/10.1002/cncr.10945
PMid:12412161

208. Ouban, A., P. Muraca, T. Yeatman & D. Coppola: Expression and distribution of insulin-like growth factor-1 receptor in human carcinomas. Human Pathology, 34, 803-808 (2003)
http://dx.doi.org/10.1016/S0046-8177(03)00291-0

209. Scartozzi, M., A. Mandolesi, R. Giampieri, C. Pierantoni, F. Loupakis, A. Zaniboni, E. Galizia, L. Giustini, R. R. Silva, R. Bisonni, R. Berardi, S. Biagetti, S. Menzo, A. Falcone, I. Bearzi & S. Cascinu: Insulin-like growth factor 1 expression correlates with clinical outcome in K-RAS wild type colorectal cancer patients treated with cetuximab and irinotecan. International Journal of Cancer, 127, 1941-1947 (2010)
http://dx.doi.org/10.1002/ijc.25193
PMid:20099280

210. Hurbin, A., M. Wislez, B. Busser, M. Antoine, C. Tenaud, N. Rabbe, S. Dufort, F. de Fraipont, D. Moro-Sibilot, J. Cadranel, J. L. Coll & E. Brambilla: Insulin-like growth factor-1 receptor inhibition overcomes gefitinib resistance in mucinous lung adenocarcinoma. Journal of Pathology, 225, 83-95 (2011)
http://dx.doi.org/10.1002/path.2897
PMid:21598249

211. Cunningham, M. P., H. Thomas, C. Marks, M. Green, Z. Fan & H. Modjtahedi: Co-targeting the EGFR and IGR-IR with anti-EGFR monoclonal antibody ICR62 and the IGF-IR tyrosine kinase inhibitor NVP-AEW541 in colorectal cancer cells. International Journal of Oncology, 33, 1107-1113 (2008)
PMid:18949375

212. Haluska, P., J. M. Carboni, D. A. Loegering, F. Y. Lee, M. Wittman, M. G. Saulnier, D. B. Frennesson, K. R. Kalli, C. A. Conover, R. M. Attar, S. H. Kaufmann, M. Gottardis & C. Erlichman: In vitro and in vivo antitumor effects of the dual insulin-like growth factor-I/insulin receptor inhibitor, BMS-554417. Cancer Research, 66, 362-71 (2006)
http://dx.doi.org/10.1158/0008-5472.CAN-05-1107
PMid:16397250

213. Haluska, P., J. M. Carboni, C. TenEyck, R. M. Attar, X. Hou, C. Yu, M. Sagar, T. W. Wong, M. M. Gottardis & C. Erlichman: HER receptor signaling confers resistance to the insulin-like growth factor-I receptor inhibitor, BMS-536924. Molecular Cancer Therapeutics, 7, 2589-98 (2008)
http://dx.doi.org/10.1158/1535-7163.MCT-08-0493
PMid:18765823    PMCid:2614316

214. Goetsch, L., A. Gonzalez, O. Leger, A. Beck, P. J. Pauwels, J. F. Haeuw & N. Corvaia: A recombinant humanized anti-insulin-like growth factor receptor type I antibody (h7C10) enhances the antitumor activity of vinorelbine and anti-epidermal growth factor receptor therapy against human cancer xenografts. International Journal of Cancer, 113, 316-28 (2005)
http://dx.doi.org/10.1002/ijc.20543
PMid:15386423

215. Dong, J., A. Sereno, D. Aivazian, E. Langley, B. R. Miller, W. B. Snyder, E. Chan, M. Cantele, R. Morena, I. B. Joseph, A. Boccia, C. Virata, J. Gamez, G. Yco, M. Favis, X. Wu, C. P. Graff, Q. Wang, E. Rohde, R. Rennard, L. Berquist, F. Huang, Y. Zhang, S. X. Gao, S. N. Ho, S. J. Demarest, M. E. Reff, K. Hariharan & S. M. Glaser: A stable IgG-like bispecific antibody targeting the epidermal growth factor receptor and the type I insulin-like growth factor receptor demonstrates superior anti-tumor activity. mAbs, 3, 273-88 (2011)
http://dx.doi.org/10.4161/mabs.3.3.15188
PMid:21393993    PMCid:3149708

216. Goldstein, N. S. & M. Armin: Epidermal growth factor receptor immunohistochemical reactivity in patients with American Joint Committee on Cancer Stage IV colon adenocarcinoma: implications for a standardized scoring system. Cancer, 92, 1331-46 (2001)
http://dx.doi.org/10.1002/1097-0142(20010901)92:5<1331::AID-CNCR1455>3.0.CO;2-M

217. Italiano, A., M. C. Saint-Paul, F. X. Caroli-Bosc, E. Francois, A. Bourgeon, D. Benchimol, J. Gugenheim & J. F. Michiels: Epidermal growth factor receptor (EGFR) status in primary colorectal tumors correlates with EGFR expression in related metastatic sites: biological and clinical implications. Ann Oncol, 16, 1503-7 (2005)
http://dx.doi.org/10.1093/annonc/mdi282
PMid:15980160

218. Sauer, T., M. G. Guren, T. Noren & S. Dueland: Demonstration of EGFR gene copy loss in colorectal carcinomas by fluorescence in situ hybridization (FISH): a surrogate marker for sensitivity to specific anti-EGFR therapy? Histopathology, 47, 560-564 (2005)
http://dx.doi.org/10.1111/j.1365-2559.2005.02252.x
PMid:16324192

219. Bibeau, F., F. Boissiere-Michot, J. C. Sabourin, S. Gourgou-Bourgade, M. Radal, F. Penault-Llorca, P. Rochaix, L. Arnould, M. P. Bralet, D. Azria & M. Ychou: Assessment of epidermal growth factor receptor (EGFR) expression in primary colorectal carcinomas and their related metastases on tissue sections and tissue microarray. Virchows Arch, 449, 281-7 (2006)
http://dx.doi.org/10.1007/s00428-006-0247-9
PMid:16865406    PMCid:1888717

220. Theodorpoulos, G. E., E. KARAFOKA, J. G. PAPAILIOU, P. STAMOPOULOS, C. P. ZAMBIRINIS, K. BRAMIS, S.-G. PANOUSSOPOULOS, E. LEANDROS & J. BRAMIS: p53 and EGFR Expression in Colorectal Cancer: A Reappraisal of 'Old' Tissue Markers in Patients with Long Follow-up. Anticancer Research, 29, 785-791 (2009)
PMid:19331236

221. Nathanson, D., A. Culliford, J. Shia, B. Chen, M. D'Alessio, Z. Zeng, G. Nash, W. Gerald, F. Barany & P. Paty: Her-2/neu expression and gene amplification in colon cancer. Int J Cancer, 105, 796 - 802 (2003)
http://dx.doi.org/10.1002/ijc.11137
PMid:12767065

222. Ramanathan, R. K., J. J. Hwang, W. C. Zamboni, F. A. Sinicrope, H. Safran, M. K. Wong, M. Earle, A. Brufsky, T. Evans, M. Troetschel, C. Walko, R. Day, H. X. Chen & S. Finkelstein: Low Overexpression of HER-2/Neu in Advanced Colorectal Cancer Limits the Usefulness of Trastuzumab (Herceptin®) and Irinotecan as Therapy. A Phase II Trial #, �. Cancer Investigation, 22, 858-865 (2004)
http://dx.doi.org/10.1081/CNV-200039645
PMid:15641483

223. Herreros-Villanueva, M., M. Rodrigo, M. Claver, P. Muñiz, E. Lastra, C. García-Girón & M. J. Coma del Corral: KRAS, BRAF, EGFR and HER2 gene status in a Spanish population of colorectal cancer. Molecular Biology Reports (2010)

224. Ioannou, N., A. G. Dalgleish, A. M. Seddon, D. Mackintosh, U. Guertler, F. Solca & H. Modjtahedi: Anti-tumour activity of afatinib, an irreversible ErbB family blocker, in human pancreatic tumour cells. British Journal of Cancer, 105, 1554-62 (2011)
http://dx.doi.org/10.1038/bjc.2011.396
PMid:21970876    PMCid:3242519

225. Modjtahedi, H., T. Hickish, M. Nicolson, J. Moore, J. Styles, S. Eccles, E. Jackson, J. Salter, J. Sloane, L. Spencer, K. Priest, I. Smith, C. Dean & M. Gore: Phase I trial and tumour localisation of the anti-EGFR monoclonal antibody ICR62 in head and neck or lung cancer. British Journal of Cancer, 73, 228-35 (1996)
http://dx.doi.org/10.1038/bjc.1996.40
PMid:8546911    PMCid:2074316

226. Lacy, M. Q., M. Alsina, R. Fonseca, M. L. Paccagnella, C. L. Melvin, D. Yin, A. Sharma, M. Enriquez Sarano, M. Pollak, S. Jagannath, P. Richardson & A. Gualberto: Phase I, pharmacokinetic and pharmacodynamic study of the anti-insulinlike growth factor type 1 Receptor monoclonal antibody CP-751,871 in patients with multiple myeloma. Journal of Clinical Oncology, 26, 3196-203 (2008)
http://dx.doi.org/10.1200/JCO.2007.15.9319
PMid:18474873

227. Watkins, D. J., J. Tabernero, H. J. Schmoll, T. Trarbach, F. J. Ramos, K. Hsu, M. Gates, J. Clark, P. LeVan & D. Cunningham: A phase II study of the anti-IGFR antibody MK-0646 in combination with cetuximab and irinotecan in the treatment of chemorefractory metastatic colorectal cancer. Journal of Clinical Oncology, 27, 4127- (2009)

228. Rowinsky, E. K., H. Youssoufian, J. R. Tonra, P. Solomon, D. Burtrum & D. L. Ludwig: IMC-A12, a human IgG1 monoclonal antibody to the insulin-like growth factor I receptor. Clinical Cancer Research, 13, 5549s-5555s (2007)
http://dx.doi.org/10.1158/1078-0432.CCR-07-1109
PMid:17875788

229. Slichenmyer, W. J., W. L. Elliott & D. W. Fry: CI-1033, a pan-erbB tyrosine kinase inhibitor. Seminars in Oncology, 28, 80-5 (2001)
http://dx.doi.org/10.1016/S0093-7754(01)90285-4

230. Garcia-Echeverria, C., M. A. Pearson & A. Marti: In vivo antitumor activity of NVP-AEW541 - A novel, potent and selective inhibitor of the IGF-IR kinase. Cancer Cell, 5, 231-239 (2004)
http://dx.doi.org/10.1016/S1535-6108(04)00051-0

231. Oliveras-Ferraros, C., A. Vall-llovera, D. Salip, A. Vazquez-Martin, S. Cufí, B. Queralt, B. Martin-Castillo, J. Brunet, R. de Llorens & J. Menendez: Evolution of the predictive markers amphiregulin and epiregulin mRNAs during long-term cetuximab treatment of KRAS wild-type tumor cells. Investigational New Drugs, 30, 1-7 (2012)
http://dx.doi.org/10.1007/s10637-010-9612-2
PMid:21161326

232. Sos, M. L., M. Koker, B. A. Weir, S. Heynck, R. Rabinovsky, T. Zander, J. M. Seeger, J. Weiss, F. Fischer, P. Frommolt, K. Michel, M. Peifer, C. Mermel, L. Girard, M. Peyton, A. F. Gazdar, J. D. Minna, L. A. Garraway, H. Kashkar, W. Pao, M. Meyerson & R. K. Thomas: PTEN Loss Contributes to Erlotinib Resistance in EGFR-Mutant Lung Cancer by Activation of Akt and EGFR. Cancer Research, 69, 3256-3261 (2009)
http://dx.doi.org/10.1158/0008-5472.CAN-08-4055
PMid:19351834    PMCid:2849653

233. Cappuzzo, F.: EGFR FISH versus mutation: different tests, different end-points. Lung Cancer, 60, 160-5 (2008)
http://dx.doi.org/10.1016/j.lungcan.2008.02.008
PMid:18367287

234. Takezawa, K., I. Okamoto, J. Tanizaki, K. Kuwata, H. Yamaguchi, M. Fukuoka, K. Nishio & K. Nakagawa: Enhanced anticancer effect of the combination of BIBW2992 and thymidylate synthase-targeted agents in non-small cell lung cancer with the T790M mutation of epidermal growth factor receptor. Molecular Cancer Therapeutics, 9, 1647-56 (2010)
http://dx.doi.org/10.1158/1535-7163.MCT-09-1009
PMid:20530710

235. Dahabreh, I. J., T. Terasawa, P. J. Castaldi & T. A. Trikalinos: Systematic review: Anti-epidermal growth factor receptor treatment effect modification by KRAS mutations in advanced colorectal cancer. Annals of Internal Medicine, 154, 37-49 (2011)
PMid:21200037

236. Jimeno, A., W. A. Messersmith, F. R. Hirsch, W. A. Franklin & S. G. Eckhardt: KRAS mutations and susceptibility to cetuximab and panitumumab in colorectal cancer. Cancer Journal, 15, 110-3 (2009)
http://dx.doi.org/10.1097/PPO.0b013e31819e3202
PMid:19390304

237. Wang, L., Q. Zhang, J. Zhang, S. Sun, H. Guo, Z. Jia, B. Wang, Z. Shao, Z. Wang & X. Hu: PI3K pathway activation results in low efficacy of both trastuzumab and lapatinib. BMC Cancer, 11, 248 (2011)
http://dx.doi.org/10.1186/1471-2407-11-248
PMid:21676217    PMCid:3141770

238. Narayan, M., J. A. Wilken, L. N. Harris, A. T. Baron, K. D. Kimbler & N. J. Maihle: Trastuzumab-induced HER reprogramming in "resistant" breast carcinoma cells. Cancer Research, 69, 2191-4 (2009)
http://dx.doi.org/10.1158/0008-5472.CAN-08-1056
PMid:19276389

Key Words: EGFR, HER-2, HER-3, HER-4, Small Molecule Tyrosine Kinsase, Monoclonal Antibody, Colorectal Cancer, Review

Send correspondence to: Helmout Modjtahedi, School of Life Sciences, Kingston University London, Kingston-upon-Thames, Surrey KT1 2EE, United Kingdom, Tel: 0044-208 5478240, FAX: 0044-208 547 7652, E-mail: H.Modjtahedi@Kingston.ac.uk