[Frontiers in Bioscience S3, 487-500, January 1, 2011]

The stem cell fitness landscape and pathways of molecular leukemogenesis

Grover C. Bagby1,2,3, Angela G. Fleischman1

1Department of Medicine, Division of Hematology and Medical Oncology, Oregon Health and Science University, Portland, Oregon 97239, 2 Knight Cancer Institute at Oregon Health and Science University, Portland, Oregon 97239, 3 NW VA Cancer Research Center, Portland, Oregon, 97239


1. Abstract
2. Introduction
3. Canonical leukemogenesis
4. Altering selection coefficients in stem cell pools
4.1. Selection Coefficients defined
4.2. Enhanced fitness of the new clone relative to cells in a normal stem cell pool
4.3. Altering the coefficient of selection by reducing fitness of stem cells in the untransformed pool
5. The fitness landscape
5.1. Lessons from lava dwellers
5.2. Molecular pathogenesis of aplastic anemia
5.3. Clonal evolution in acquired aplastic anemia
5.4. Molecular pathogenesis of Fanconi anemia
5.5. Overproduction of cytokines by FA cells
5.6. Bad stem cell pools in marrow failure states
6. Clonal evolution in Fanconi anemia
6.1. Adaptive responses
6.2. Myelodysplasia and AML
7. Generalization of the model
7.1. JAK2 mutations and myeloproliferative diseases
8. Implications of clonal adaptation
8.1. Oncogene addiction
8.2. Oncogenes vs. non-oncogenes: distinguishing "passengers" from "drivers"
8.3. Leukemia Prevention
9. Acknowledgements
10. References


The relative risk of clonal evolution to either myelodysplasia (MDS) or acute myelogenous leukemia (AML) is high in patients with chronic bone marrow failure. From 10 to 20% of acquired aplastic anemia survivors will develop clonal evolution within the decade following their diagnosis as will 40% of patients with some of the inherited bone marrow failure syndromes. Studies on bone marrow failure states have provided some perspective on molecular pathogenesis of marrow failure and have also provided insights on the adaptive nature of clonal evolution. We review the scientific evidence validating this model, emphasize the importance of the fitness landscape in the stem cell pool, outline the clinical and investigative implications of the model, suggest that the lack of fitness in the starting pool accounts for the phenomenon of oncogene addiction, promote the value of the model for the evaluation of prevention strategies, and argue that experiments focusing attention on the relative phenotypes of neoplastic stem cell clones and pools of unfit stem cells from which they evolved will provide a useful paradigm of carcinogenesis in general.


Acute myeloid leukemic clones evolve from somatically mutated hematopoietic stem cells (HSCs) or progenitors (HPCs) that have acquired (or aberrantly retained) the capacity self- replicate but have lost the capacity to give rise to myeloid precursor cells capable of undergoing orderly terminal differentiation. Recent evidence from high-density SNP arrays and massively parallel DNA sequencing analyses of AML samples have identified multiple point mutations(1) and significant alterations in gene copy number(2) even in samples that appear normal by standard metaphase cytogenetic analysis. Recurrent mutations have been identified in AML and the identification of some of them can help with assessments of prognosis.(3-7) Unfortunately, less is known about the function of the mutant proteins or the consequence of gene inactivation and, in light of the enormous case-to-case genomic heterogeneity and multiplicity of genomic changes, nothing is known about the temporal order of appearance of genomic alterations during the course of clonal evolution; that is, from the starting point of the very first genetic change.

Many published studies have revealed factors that likely influence disease progression in AML but until recently, few reliable in vivo models of myeloid leukemogenesis existed that might shed light on early genetic events in this process. Only a clear picture of the first molecular events that ignite clonal evolution in HSCs will pave the way to the development of rational approaches to leukemia prevention, particularly in patients at high risk. Fortunately, there are now new genetic paradigms of spontaneous myeloid leukemogenesis, (8, 9) that can be used to illuminate ordered events in leukemic clonal evolution in bone marrow failure states. These models have also confirmed earlier predictions that when clones evolve in the context of bone marrow failure states they do so by adapting to the environmental stresses to which all other cells in the stem cell pool were vulnerable.(10-12)


Dominant acting oncogenes are clearly involved in the molecular pathogenesis of a variety of hematologic neoplasms and for cases in which promiscuous kinase activation is the cause, knowledge of the key pathway in individual cases has enormous therapeutic significance.(13-15). The capacity of aberrantly regulated or mutated genes to transform hematopoietic cells and to induce stem cell expansion in vitro and in vivo has been demonstrated in many cases, leading to the presumption that the function of the oncogene is sufficient to account for the process of leukemogenesis in nature. This presumption is overdrawn because the experimental model usually involves the ectopic expression of the gene in question. In addition, it cedes to the activated oncogene the capacity to function as a complete leukemogen in a pool of stem cells that are completely normal and in all environmental contexts. In fact, few studies have focused on the possibility that, in nature, the stem cells in the non-neoplastic pool may be dysfunctional and only because they are unfit can the evolutionary process proceed.

Moreover, it is increasingly clear that genes (HOXA9 for example) whose activation regularly occurs when AML clones evolve(16) and are therefore considered to be leukemogenic(17, 18) are often insufficient, when ectopically over-expressed on their own, to induce leukemic transformation.(19, 20) Instead, such genes maintain key cellular functions or encode critical co-factors upon which other leukemogenic factors depend.(21) They may also protect a cell in which the gene is highly expressed from the vicissitudes of the environment, and may, only under certain conditions of stress, allow that cell to acquire a competitive survival advantage.(22)

Highly informative studies on human cells have shown that some genomic alterations considered to be classically involved in leukemogenesis are insufficient, on their own, to account for the outgrowth of leukemia clones. For example, in studies by Greaves and his colleagues, the translocation t8;21 found in the leukemic cells of children with AML was also found to have existed in prenatal life indicating that this classical leukemic marker may have provided a key "parental phenotype" in the stem cell pool but was insufficient to induce rapid clonal evolution.(23) This notion is confirmed by a related study from the same group reporting that the "leukemogenic" translocations TEL-AML1 and AML1-ETO can be found in cord blood samples of normal neonates at a frequency at least two orders of magnitude greater than the prevalence of the leukemia that sorts with the translocation.(24)

Based on their analyses of TEL-AML1-transduced cord blood cells, the group argues that TEL-AML1 functions as a first-hit mutation by endowing a cell with altered self-renewal and survival properties(25) and that the early TEL-AML1 clone is truly preleukemic but requires some additional environmental events to occur before the mutation leads to clonal evolution. Based on these and like studies and on results of recent high-throughput genomic analyses of AML cells(1, 2), it is obvious that complex molecular interdependencies exist during the course of clonal evolution to AML and that the earliest changes are necessary but not sufficient for the full development of the neoplastic clone. What then is the relevant function of the early molecular aberrations and how does clonal evolution begin to occur? If they are weak mutations in the classic sense(26) what does the environment contribute to their selectability? From studies we have conducted on the rare bone marrow failure syndrome Fanconi anemia,(9, 12) using both human and murine hematopoietic cells, we believe that clonal evolution, at least in that particular context, meets every standard of a Darwinian selection process(27) and that this disease provides a robust opportunity to identify early genetic events in leukemogenesis.


4.1. Selection coefficients defined

Applied legitimately to both sexual (e.g. mammalian) and asexual (e.g. HSC) populations, the coefficient of selection ("s") represents the proportionate reduction in the pool contribution made by a specific genotype, relative to the contribution made by another genotype. That is, "s" expresses the relative advantage or disadvantage of specific traits with respect to survival and expansion. A selection coefficient may have a value from zero to one. If s=0 a selected genotype is neutral compared to the favored phenotype. Increasing "s" from 0 to 1 describes decreasing fitness of the genotype in question. Therefore, if we apply this standard to the work on t8;21 in normal prenatal cells,(24) and grant that at least one HSC carries the translocation, that cell can be assigned s=0. The neutrality of this cell in its environment raises important questions. Was the translocation the first molecular event that occurred in an untransformed stem cell? If not, what event initially sent a mutant stem cell down the path of clonal evolution? What role if any does the macro- or microenvironment play in the process?

There are two ways that selection coefficients can be altered to favor clonal evolution. The first, and most commonly promoted in the literature is the circumstance in which the new clone arises in the context of a normal pool of stem cells and at some point acquires a significant growth advantage by acquiring new mutations that alter its response to environmental cues in favor of growth or differentiation blockade. Inflammation is commonly invoked as a driver.

4.2 . Enhanced fitness of the new clone relative to cells in a normal stem cell pool

There is abundant clinical and experimental evidence to support the idea that inflammation plays a role in the molecular pathogenesis of neoplastic processes. Patients with ulcerative colitis are at high risk for the development of colon cancer(28) and rodent models of colon cancer(29) have been developed which are tightly associated with diffuse colitis resembling ulcerative colitis in humans.(30) Colitis is inducible by exposing mice to dextran sulfate sodium and in this context, tumors develop.(31) Interestingly, genetic or pharmacological inhibition of TNFα signaling reduces both inflammation and tumorigenesis.(31) There are a number of other cancers that arise in the context of inflamed tissues including hepatitis C virus induced hepatocellular carcinoma(32, 33), adenocarcinoma of the esophagus associated with Barrett's esophagus,(34) gastric cancer associated with Helicobacter pylori infection,(35) and others. Some have even argued that inflammation should become a hallmark of cancer as important as uncontrolled growth and metastasis.(36)

Notwithstanding the evidence that the inflammatory process is capable of promoting cancer progression,(37-39) and the theoretical potential for components of the inflammatory response (e.g. reactive oxygen species (ROS)) to induce DNA damage,(40-42) there is no evidence that inflammation per se is sufficient to account for the earliest steps of clonal evolution. This is in large part because the intense focus on the inflammatory response has strangely ignored the fundamental principle that inflammation is, more often than not, a consequence, not a primary cause of tissue damage. Hepatitis C virus, for example, increases apoptotic responses in infected hepatocytes,(43) and the apoptotic fraction of colonocytes is increased in ulcerative colitis.(44) The landscape in those organ systems includes unfit pools of pressured non-transformed cells from which a mutant clone arises but the condition of the cells in these pools is commonly ignored as a determinant in clonal evolution. Environmental factors are capable of altering clonal selectability from moment to moment changing any given mutation from weak and physiologically insignificant to strongly selectable and unambiguously "beneficial" at least in the short term and at the level of a single cell. Therefore, the fitness landscape simply can't be ignored.

4.3. Altering the coefficient of selection by reducing fitness of stem cells in the untransformed pool

A second way of altering selection coefficients is by a reduction in fitness in the general stem cell pool. The evolutionary impact of genetic change is determined by comparing fitness of one genotype to that of another. For studies on carcinogenesis normal cells are most often used as a reference point. This isn't always appropriate. Normal cells vs. a mutant clone might have an "s" of zero, but when a less fit pool of cells (a pool of unfit hepatitis C infected hepatocytes for example) is compared to the same mutant, their score might be closer to 0.5 or more. Stated another way, when a mutant clone is compared to a normal population a given genotype might be insignificant, but when compared to cells in an unfit pool under attack from factors in the microenvironment, it might be significantly more fit. Naturally the increase in fitness would depend upon a match between the acquired genetic change (stochastic) and the stressful challenge the mutation relieves. The mutation must precisely match and relieve the stress that makes the pool unfit in the first place. Under these environmental conditions, the mutation would meet the standard of a "beneficial" mutation(45) at the cellular level although clearly for the whole organism it would be precisely the opposite. Evolution of mutants from a globally unfit pool is a general mechanism of clonal evolution that we see in Fanconi anemia and will be described in more detail below. An interaction between mutant stem cells and their microenvironment plays a seminal role in defining the fitness landscape in this disease and it is this aberrant relationship that defines the molecular pathogenesis of both bone marrow failure and leukemic clonal evolution.

5. The Fitness Landscape

5.1. Lessons from lava dwellers

The molecular genetics of adaptive coat color variation in rock pocket mice is an instructive example. These animals are light-colored and live in light colored environments. Dark colored mice have habitats on darker colored lava beds. Mutations in the melanocortin-1-receptor gene, Mc1r, are responsible for melanism in the lava-dwellers.(46) In a laboratory, the dark colored mice have no inherent advantage over the lighter ones. They are equally fit congenic strains but in the wild the coefficient of selection is massively altered such that on lava beds s=1 (a lethal score) for the light colored mice because they can be more easily seen by predatory birds and mammals.(46, 47) In the absence of predators, scores for both absolute and relative fitness, concepts that can be defined mathematically (reviewed in (48)), of these two strains are identical but both scores differ in the real world. In effect, the environment does its work to select the fit population not by influencing directly that population but by purging its unfit competitors. There is evidence that this is true not only for bacteria in which adaptation to antibiotic challenge results in resistance(49, 50) but for mammalian cells as well.(51) This Darwinian model fits perfectly with results of studies on stressed HSCs, namely those found in the bone mice and humans with bone marrow failure.

5..2. Molecular Pathogenesis of Aplastic Anemia

Acquired aplastic anemia is most often an autoimmune disease. The evidence from a number of laboratories, recently summarized by Young et al, (52) has revealed that; (1) aberrantly activated oligoclonal T-cell populations(53) suppress hematopoiesis by releasing cytokines (importantly IFNg and TNFa ) (2) these cytokines and other factors induced by them cause apoptotic responses in hematopoietic stem and progenitor cells, (3) clinical responses to immunosuppressive therapy vary directly with the power of the treatment to suppress aberrant T-cell function,(54) and (4) immune mediated bone marrow failure can be modeled in mice and in that model monoclonal antibodies to TNFa and IFNg prevent fatal aplasia.(55) Recent gene expression microarray analysis confirms on a genome wide scale that T-cell populations(56) are on the attack and that the progenitor cell pool is suffering as a consequence.(57)

5.3. Clonal evolution in acquired aplastic anemia

Stem cells assaulted by cytotoxic lymphoid populations(54) represent perfect models of a disadvantaged population. Unless the offending T-cell population is eradicated or inactivated, the selective pressure they exert on the stem cell pool would favor the evolution of any somatically mutated stem cell that had acquired, by virtue of the mutation, the capacity to resist the attack of T-cells. An identical somatic mutation might occur randomly in a single cell in an otherwise normal stem cell pool. In this case, because the selection coefficient is zero, clonal evolution would not be favored. It is precisely this situation that might explain how potentially leukemic clones can be found during normal fetal development yet not raise their heads even later in life.(24) However, if some environmental stressor were to disadvantage the cells in the normal pool, the situation could then favor clonal evolution. The environmental challenge therefore reduces fitness in the stem cell pool and creates an opportunity for selection of somatic mutants or epigenetically altered stem cells to emerge - mutant cells that may have existed for years in advance of the environmental insult. The most compelling experimental evidence in support of this paradigm derives from studies on humans and mice with an inherited form of bone marrow failure, Fanconi anemia.

5.4. Molecular pathogenesis of fanconi anemia

Fanconi anemia is a rare autosomal recessive (and in the case of FANCB, X-linked) disease characterized by congenital skin and skeletal anomalies, bone marrow failure, short stature, and high relative risks of acute myelogenous leukemia and epithelial malignancies.(58-60) Biallelic inactivation of any one of at least 13 genes are known to be responsible for this disease.(58, 61) Excessive chromosomal breakage in response to DNA crosslinking agents was one of the first reliable in vitro disease markers(62) and, indeed, forms the basis of the current diagnostic test. Consequently, most of the scientific work on this rare disorder has focused upon chromosomal instability phenotype. However, Fanconi himself observed that this disease has a strong phenotype of hematopoietic failure(63) and hematologic defects are the most consistent abnormalities seen in practice. Virtually all patients will exhibit some degree of bone marrow hypocellularity, albeit of varying severity, and up to 40% of children and young adults with FA will exhibit signs of clonal evolution in the bone marrow. This is a process in which aberrant HSCs with acquired genetic alterations self-replicate with more success than their competitors and give rise to progeny that overtake the bone marrow leading to myelodysplasia (MDS) and acute myelogenous leukemia (AML). (64, 65)

The historical presumption of the FA research community has been that the DNA damage phenotype is the direct cause of stem cell failure, but recently biochemical pathways of hematopoietic dysfunction have been discovered that can be, in some cases, formally uncoupled from DNA damage.(66, 67) More than 15 years ago in seeking to unravel the molecular pathogenesis of marrow failure in FA, we took notice of reports of parents and referring pediatricians that viral infections in children with this disease were often followed by periods of prolonged pancytopenia. For that reason, we considered that this aberrant response reflected an unusual sensitivity of hematopoietic progenitor cells to inflammatory cytokines that evolve in response to the infection. We also supposed that recurrent inflammatory events in patients with FA might sweep through the stem cell pool and result in its contraction. As will be described below, this turned out to be the case. It is also now very clear that such inflammatory events can serve as classical "selective sweeps" permitting the evolution of neoplastic clones.(9)

Hematopoietic cells from children and adults with Fanconi anemia and in mice nullizygous for Fancc not only release more TNFa in response to TLR ligation and in the ground state(68-70) but hematopoietic progenitor cells are also hypersensitive to TNFα and other well known growth suppressive cues. Specifically, the growth of FANCC- and Fancc-deficient progenitor cells is suppressed by very low doses of IFNγ, TNFα, mip1α and TRAIL.(71-75) HSCs are also hypersensitive to IFNγ because continuous infusions of that cytokine enhance engraftment of gene-corrected HSCs in competitive repopulation experiments not only in Fancc-deficient mice but in Fancg and Fanca deficient mice as well.(76, 77) Similar hypersensitive responses occur in FA progenitors and stem cells exposed to TNFα through direct exposure to that cytokine or by exposure to TLR-activating agents that induce its overproduction.(78, 79) While apoptotic responses seem to be one pathway of suppression by cytokines in these cells,(71, 80, 81) more recently we have also noted that TNF suppresses the replicative activity of Fancc-deficient multipotential progenitor cells (unpublished). Either way, FA stem cell pools are unambiguously unfit.

Some of the biochemical mechanisms of this hypersensitivity are now being clarified. For example, two serine/threonine kinases are involved in TNFα hypersensitivity because their activity is directly influenced by FA proteins. One is the protein kinase PKR a key molecular effector of the anti-viral response. The other is the apoptosis signal regulating kinase 1 (Ask1).(80, 82-84) Suppression of either one of these kinases relieves the cytokine hypersensitivity phenotype in vitro.

5..5. Overproduction of cytokines by FA cells

To add fuel to the fire, FA mononuclear phagocytes over-produce TNFα. Schultz and Shahidi(85) were the first to describe elevations of TNFα levels in serum of children with Fanconi anemia but the significance of and mechanisms that explain those findings have only recently emerged. Pang's group reported that Fancc-/- mice treated with endotoxin (lps) had higher mortality rates than wild type mice, had higher serum levels of TNFa and IL-6, and developed profound bone marrow suppression in response to lps that was formally attributed to an effect of TNFa (anti-TNFα antibodies protected FA hematopoietic cells).(78) They also showed that transplantation of HSCs from wild type mice protected Fancc-/- mice from endotoxin-induced TNF-overproduction and mortality, clarifying that both the TNF-hypersensitive cell population and the TNF-overproducing population were of hematopoietic origin.(78) What biochemical mechanisms underlie the overproduction phenotype have not been fully clarified but one pathway of significance seems to be that of Toll-like receptor 8 (TLR8) which is hyper-activated by the ligand R848 in FANCC- and Fancc-deficient mononuclear phagocytes. (70)

5.6. Bad stem cell pools in marrow failure states

In summary, abnormalities of stem cell self-renewal(86) and survival(9, 71, 82, 84) are found in patients with both acquired and inherited aplastic states. Both patient populations have high relative risks of clonal evolution to MDS and AML and there is strong evidence (indirect in humans and direct in mice) that the clones appear in response to aberrant production of or responses to suppressive cytokines or both. In acquired aplastic anemia the stem cell stress depends upon clones of T-cells that overproduce factors that result in stem cell death and loss of self-replicative potential.(52, 87) In Fanconi anemia the production of some of the same factors is increased because the normal FA proteins set response thresholds for TLR ligands including R848(70) and endotoxin(78)). In addition, the FA stem cell pool is inherently hypersensitive to those factors because the normal FA proteins somehow set response thresholds for exactly the cytokines over-expressed in auxiliary cells.(59) Experimental evidence supporting stem cell stress in other inherited marrow failure syndromes is not as robust, but preliminary studies support the idea that highly disadvantaged stem and progenitor cells exist in the hematopoietic microenvironment in these disorders as well.(88-90) Because of their lack of fitness, the selection coefficient is such that mutated stem cell clones have acquired the capacity to rectify the abnormal relationship of the defective stem cell with its environment. These clones will have a huge competitive advantage when they are in competition with the unfit cells but might not have an advantage at all if they are tested against normal ones.

6. Clonal Evolution in Fanconi Anemia

6.1. Adaptive responses

Fanconi anemia stem cells, with time, will either adapt or perish. There are two pathways for adaptation. The perfect adaptive response in a pressured FA stem cell is, in fact, seen in nature and accounts for a phenomenon known as mosaicism. In this condition, a single HSC undergoes a corrective genetic rearrangement or mutation that corrects one of the FA alleles. This can happen through compensatory missense mutations, gene conversion, or intergenic crossovers.(91-93) In these cases, it isn't uncommon for the bone marrow to be dominated by the new clone and for hematopoiesis to be either normal or nearly normal.(94) Unlike the uncorrected mutant cells, the progeny of the clone are: (a) resistant to mitomycin C (MMC), (b) respond to TLR ligation normally vis-à-vis TNFα production, and (c) show perfectly normal responses to suppressive cytokines (Table 1). To emphasize some important points to be deduced from these experiments of nature, we summarize here experiments conducted using hematopoietic cells and fibroblasts from twins with biallelic mutations of FANCA.(94)

Monozygotic twin sisters were born with skeletal and cutaneous stigmata of FA but without hematologic defects. Mitomycin C tests of peripheral blood lymphocytes showed no evidence of excessive chromosomal breakage diagnostic of FA. Because fibroblasts did show MMC-induced breakage, they were clearly somatic mosaics for mutations in the FANCA gene. In skin fibroblasts, molecular analysis revealed a frameshift causing deletion in exon 27 (2555DeltaT) and an exon 28 missense mutation (2670G >A / R880Q). The latter resulted in reduced function of the mutant FANCA (R880Q) protein. An acquired exon 30 missense change (2927G >A / E966K) was detected in the hematopoietic cells of both sisters, but was not found in fibroblasts of the patients or of the parents. This compensatory mutation existed in cis with the maternal exon 28 mutation, and restored the function of the resulting protein in hematopoietic cells.(94) Neither sister has had abnormal blood counts for more than 3 decades.

There are some profound implications of such experiments of nature. First, because the compensatory mutation was identical in both twins, this de novo "corrective" mutation occurred prenatally in a single HSC in one twin and the progeny of this HSC repopulated the blood lineages of both sisters through a shared intrauterine circulation. Secondly, because the corrected clone replaced the entire marrow of both twins indicates that FA stem cells are unfit early in development (a conclusion supported experimentally by recent studies on embryonic stem cells(86)) and that the selection coefficient in the pool was high. Third, because one stem cell was capable of taking over the entire marrow of both twins suggests that effective gene therapy in patients with FA might require successful transduction of only a small number of stem cells.(94)

6.2. Myelodysplasia and AML

The second "adaptive" pathway for FA stem cells results in clonal evolution to either myelodysplasia or acute myelogenous leukemia. While the "adaptive" steps might assure the survival of the new stem cell and its progeny, the clonal progeny are not normal and reveal multiple abnormalities of growth and differentiation control. The syndromes that ultimately result from expansion of the neoplastic clones are often untreatable and more often fatal than not. It therefore seems reasonable, for purposes of this discussion, to consider this type of response as "maladaptive" and the category of mutations "pseudo-beneficial."

To emerge as a new clone, the unfit stem cell must overcome the aberrant pathways that reduced its fitness in the first place. This does occur in humans and has been modeled in mice.(9, 95, 96) For example, as mentioned above, TNFα hypersensitivity exists in progenitor cells of patients and mice with Fanconi anemia in the hypoplastic phase.(9, 12, 78, 79) However, in longitudinal studies on FA patients who enter the phase of clonal evolution to myelodysplasia, we find that the progenitor cells exhibit either resistance to TNFα or a paradoxical proliferative response in vitro. Likewise, in FA siblings discordant for clonal evolution, cytokine hypersensitivity exists in the hematopoietic progenitor cell population from the sibling without clonal evolution but resistance or a paradoxical (replicative) response is found the progenitors of the sibling with MDS.(12)

Unlike the example of mosaicism, these are not perfectly adaptive responses because: (a) the progenitor cells are more resistant to TNFα than even normal progenitor cells, (b) TNF-α production by the neoplastic mononuclear phagocytes remains very high in response to TLR ligation (unpublished), and (c) the clonal progeny show diagnostic chromosomal breakage responses to MMC (Table 1). In effect, the selection of neoplastic progenitors has resulted in exploitation of the macrophage defect by adapting in a way that leads not to their demise but to their outgrowth and survival. The neoplastic clone has a genotype that is "beneficial" to the survival of the stem cell, but is catastrophic for the host because it is fundamentally a new population that has learned how to grow in response to suppressive cues, overproduces the cue, and retains its genetic instability.

This process has been modeled in mice. A number of groups have observed acquired cytokine resistance and clonal evolution in murine models of FA.(8, 9, 96, 97). In one of these models, murine Fancc-/- stem cells and their progeny were cultured ex vivo for up to 90 days. During this culture period in some instances TNFα -resistant cytogenetically abnormal clones appeared. These clones had the capacity to induce ongoing clonal evolution to AML in transplanted mice.(9) That the appearance of these clones depends upon the continued presence of TNFα(9) emphasizes the importance of selective pressure in accelerating this process. That we have universally seen TNF-resistance in clonally evolved FA progenitor cells suggests that the cytokine hypersensitive phenotype is required for clonal evolution. It is therefore reasonable to expect that the development of cytokine resistance would be one of the earliest steps in myeloid leukemogenesis.

We do not argue that the change is sufficient to initiate the entire leukemogenic process. In addition, over time the new clone may also become resistant to other factors as well,(98) a phenomenon that would only make the neoplastic clone even more capable of competing against the disadvantaged stem cells. Nor would we argue that clonal evolution is always a formally genetic process because epigenetic events have been described as factors in the evolution of hematologic neoplasms as well.(99-101) In fact, genetic loss and epigenetic silencing may cooperate in some instances.(99, 100, 102) In myeloid leukemic clones with allelic losses due to chromosomal deletions, for example, the retained allele can be suppressed epigenetically(103) resulting in a functional loss of heterozygosity.

7. Generalization of the model

Unfit stem cell pools plays an important role as a breeding ground for maladaptive mutations in the context of bone marrow failure. Because the development of malignant neoplasms is often an outcome of chronically damaged tissues, we argue that the fitness landscape in other stressed stem cell pools might play a role in carcinogenesis in general. We suspect that oncogenic mutations that lead to other hematologic malignancies might evolve in a like context; namely in pools of disadvantaged stem cells.

7.1. Jak2 mutations and myeloproliferative diseases

An activating mutation in the tyrosine kinase JAK2 (V617F) is identified in the majority of patients with Philadelphia chromosome-negative myeloproliferative neoplasms (MPN).(104-108) This mutation arises at the level of the hematopoietic stem cell(109) and results in expansion of one or more of the myeloid lineages each of which retains the ability to execute a complete differentiation program. Animal models of this disease abound. A polycythemia vera (PV)-like disease with secondary myelofibrosis arises in lethally irradiated mice transplanted with bone marrow transduced with JAK2 V617F retroviral vectors.(110-112) Transgenic(113) and knock-in mice expressing JAK2 V617F or Jak2 V617F under the influence of the endogenous Jak2 promoter, (114-116) develop an ET or PV-like MPN demonstrating that in mice the JAK2 V617F mutation is sufficient to induce a myeloproliferative phenotype. It should be emphasized, however, that the design of these experiments does not address the earliest steps in leukemic evolution in which a single cell and its progeny gain a competitive advantage. Admitting to the speculative nature of the idea, we suggest that the MPNs might evolve in ways analogous to the evolution of clones in patients with marrow failure syndromes, that is, specifically from unfit pools of HSCs.

Clinically relevant cytopenias have not been recognized as a prodromal feature of MPN so how could the leukemogenesis model we have described for the marrow failure syndromes be conceivably applied to these diseases? First, substantial stem cell defects can occur in nature without attendant changes in blood counts in the ground state.(117) Only by providing environmental challenges to those pools can the vulnerability of stem cells and their progeny be revealed.(9, 76-79) Secondly, in every murine model of MPNs described, some sort of environmental stress exists precisely at the point clones might take hold. Thus, JAK2 V617F might have provided an advantage only in the context of transiently disadvantaged stem cells. For example, in both of the recent descriptions of conditional knock-in models, a pool of normal stem cells was transiently exposed to high levels of IFNγ (induced by the polyI-polyC required to activate Mx dependent Cre) so the initial outgrowth of JAK2 V617F expressing cells cannot be said to have occurred in an unstressed landscape. Indeed, exposure to pI:pC would likely have been sufficient to suppress expansion of Fanconi stem cells.(76, 77) In secondary transplants however, the landscape would have improved (or at least normalized) which might explain why there was no competitive advantage seen in the studies by Li et al.(115) However, even in secondary transplants, the cytokine storm induced by lethal radiation(118) could be a sufficient early stressor to induce the selective emergence of stem cells that express the mutant JAK2 (provided the mutant protected stem cells from one or more of the suppressive cytokines). Therefore, because none of the models tested begin with a single mutant cell in an unperturbed ground state environment, they do not directly address the molecular pathogenesis of the earliest steps in clonal evolution.

No one can sanely argue that in MPN patients the JAK2 V617F mutant cells have no advantage compared to the JAK2 wild-type cells in that patient. However, it is equally true that no one can yet argue, at least until the definitive experiments are done, that JAK2 wild type cells in MPN patients are perfectly fit. We believe that in humans the unmutated stem cells might well be unfit and that the evolution of the JAK2 mutant clone might represent an adaptive response. In fact, some genetic observations provide opportunities to test this notion directly. First, there exists a familial predisposition to acquire MPN. Nearly 8 percent of patients will have a strong family history of MPN.(119) Second, a specific JAK2 haplotype (termed 46/1) is strongly associated with JAK2V617F+ MPN, with a relative risk of 2.6.(120-122) and, interestingly, healthy controls with this haplotype have decreased granulocyte macrophage colony growth as compared to controls,(122) compatible with the notion that this haplotype (and the predisposition to acquire MPN) is associated with subclinically unfit progenitor and stem cell pools.


8.1. Oncogene addiction

The effectiveness of molecularly targeted agents (some of which can induce regression of a mutant clone but not suppress normal stem cells) has posed some challenging questions. Why do cancers that depend upon one wayward gene to maintain its neoplastic state simply die when that one gene is inactivated when it ought to simply suppress the proliferative advantage that the mutation confers? This phenomenon of "oncogene addiction"(123-125) can be modeled in conditional "oncomice" in which oncogene deprivation can induce sustained regression via induced differentiation or programmed cell death.(124) Whether this model represents the situation in nature is unclear. One alternative explanation is that suppression of oncogene function in evolved neoplastic clones can be lethal because the stem cells that were transformed by that oncogene were unfit to start with and required the activation of the oncogene to survive in the first place.

8.2. Oncogenes vs. non-oncogenes: distinguishing "passengers" from "drivers"

To credential mutations of tyrosine kinase alleles as "driver" mutations, a common and fairly reliable approach is to determine whether ectopic expression of the mutant in cytokine dependent murine hematopoietic cells results in; (a) a phenotype of cytokine independence and (b) enhancement of or constitutive activation of tyrosine kinase activity.(126-128) A mutation that fails to meet these standards is considered to be more likely a "passenger" mutation (one plays no role in disease pathogenesis).(128) There are exceptions to this rule. For example, some BRAF mutants that have lost catalytic activity are known to promiscuously activate CRAF so the downstream consequences are identical to those ignited by BRAF mutants with elevated kinase activity.(129) In addition, and more to our point, mutations might not be sufficient to induce factor independent growth but might be sufficient to protect exposed cells from perishing under stressful conditions. The experimental approach would be difficult because discovering the right mix of inhibitory factors and environmental conditions (that a potential passenger mutation might resist) would require a "fishing expedition" of sorts but with high throughput screening strategies, the task would not be unachievable. Adding such experiments to the process of credentialing mutant enzymes might provide evidence of growth and survival advantages in cells expressing mutant enzymes that have no catalytic activity.

8.3. Leukemia Prevention

Systems biology experiments can now be simply done using stem cell pools at high risk of AML and MDS and as a result a clearer picture of the temporal events that precede clonal evolution will be soon apparent. Even if the nature of the key stem cell pool stressor is not known, by identifying early molecular alterations in the march toward clonal evolution, one can backtrack to narrow the list of what those stressors might be. For example, if an early alteration in a stem cell pool suppressed expression of a receptor for inhibitory factor X, one could then directly test the notion that factor X was somehow initially contributing to the suppression of fitness in the parental stem cell pool. So unique signatures of adaptation ought to lead to the identification of factors that contribute to the reduction of fitness in stem cell pools. Once these factors are credentialed, they naturally would become molecular targets for prospective studies on leukemia prevention. It is this prospect that excites us the most.


This work was supported in part by NIH grants CA138237 and HL048546 (GCB), the VA Merit Review Award (GCB) and 5T32HL007781 (AGF).


1. Elaine Mardis, Li Ding, David Dooling, David Larson, Michael McLellan, Ken Chen, Daniel Koboldt, Robert Fulton, Kim Delehaunty, Sean McGrath, Lucinda Fulton, Devin Locke, Vincent Magrini, Rachel Abbott, Tammi Vickery, Jerry Reed, Jody Robinson, Todd Wylie, Scott Smith, Lynn Carmichael, James Eldred, Christopher Harris, Jason Walker, Joshua Peck, Feiyu Du, Adam Dukes, Gabriel Sanderson, Anthony Brummett, Eric Clark, Joshua McMichael, Rick Meyer, Jonathan Schindler, Craig Pohl, John Wallis, Xiaoqi Shi, Ling Lin, Heather Schmidt, Yuzhu Tang, Carrie Haipek, Madeline E. Wiechert, Jolynda V. Ivy, Joelle Kalicki, Glendoria Elliott, Rhonda E. Ries, Jacqueline E. Payton, Peter Westervelt, Michael Tomasson, Mark Watson, Jack Baty, Sharon Heath, William Shannon, Rakesh Nagarajan, Daniel Link, Matthew Walter, Timothy Graubert, John DiPersio, Richard Wilson and Timothy Ley: Recurring mutations found by sequencing an acute myeloid leukemia genome. N Engl J Med 361, 1058-1066 (2009)

2. Matthew Walter, Jacqueline Payton, Rhonda Ries, William Shannon, Hrishikesh Deshmukh, Yu Zhao, Jack Baty, Sharon Heath, Peter Westervelt, Mark Watson, Michael Tomasson, Rakesh Nagarajan, Brian O'Gara, Clara Bloomfield, Krzysztof Mrozek, Rebecca Selzer, Todd Richmond, Jacob Kitzman, Joel Geoghegan, Peggy Eis, Rachel Maupin, Robert Fulton, Michael McLellan, Richard Wilson, Elaine Mardis, Daniel Link, Timothy Graubert, John DiPersio and Timothy Ley: Acquired copy number alterations in adult acute myeloid leukemia genomes. Proc Natl Acad Sci U S A 106, 12950-12955 (2009)
PMid:19651600    PMCid:2716381

3. Susanne Schnittger, Wolfgang Kern, Claudia Tschulik, Tamara Weiss, Frank Dicker, Brunangelo Falini, Claudia Haferlach and Torsten Haferlach: Minimal residual disease levels assessed by NPM1 mutation-specific RQ-PCR provide important prognostic information in AML. Blood 114, 2220-2231 (2009)

4. Lars Bullinger, Konstanze Dohner, Raphael Kranz, Cristoph Stirner, Stefan Frohling, Claudia Scholl, Young Kim, Richard Schlenk, Robert Tibshirani, Hartmut Dohner and Jonathan Pollack: An FLT3 gene-expression signature predicts clinical outcome in normal karyotype AML. Blood 111, 4490-4495 (2008)

5. Susanne Schnittger, Tobias Kohl, Torsten Haferlach, Wolfgang Kern, Wolfgang Hiddemann, Karsten Spiekermann, and Claudia Schoch: KIT-D816 mutations in AML1-ETO-positive AML are associated with impaired event-free and overall survival. Blood 107, 1791-1799 (2006)

6. Claude Preudhomme, Christophe Sagot, Nicolas Boissel, Jean-Michel Cayuela, Isabelle Tigaud, Stéphane de Botton, Xavier Thomas, Emmanuel Raffoux, Charlotte Lamandin, Sylvie Castaigne, Pierre Fenaux, Hervé Dombret and ALFA Group: Favorable prognostic significance of CEBPA mutations in patients with de novo acute myeloid leukemia: a study from the Acute Leukemia French Association (ALFA). Blood 100, 2717-2723 (2002)

7. Rose Padua, Barbara Guinn, Ala Al-Sabah, M. Smith, Christine Taylor, Tom Pettersson, S. Ridge, G. Carter, D White, David Oscier, S. Chevret, and Robert West: RAS, FMS and p53 mutations and poor clinical outcome in myelodysplasias: a 10-year follow-up. Leukemia 12, 887-892 (1998)

8. Anna Pulliam-Leath, Samantha Ciccone, Grzegorz Nalepa, Xiaxin Li, Yue Si, Leticia Miravalle, Danielle Smith, Jin Yuan, Jingling Li, Praveen Anur, Attilio Orazi, Gail Vance, Feng-Chun Yang, Helmut Hanenberg, Grover Bagby and D. Wade Clapp: Genetic disruption of both Fancc and Fancg in mice recapitulates the hematopoietic manifestations of Fanconi anemia. Blood (2010) (Epub ahead of print)

9. June Li, Daniel Sejas, Xiaoling Zhang, Yuhui Qiu, Kalpana Nattamai, Reena Rani, Keaney Rathbun, Hartmut Geiger, David Williams, Grover Bagby, and Qishen Pang: TNF-alpha induces leukemic clonal evolution ex vivo in Fanconi anemia group C murine stem cells. J Clin Invest 117, 3283-3295 (2007)
PMid:17960249    PMCid:2040318

10. Grover Bagby: Discovering early molecular determinants of leukemogenesis. J Clin Invest 118, 847-850 (2008)
PMid:18292805    PMCid:2248429

11. Fulu Liu, Ghada Kunter, Maxwell Krem, William Eades, Jennifer Cain, Michael Tomasson, Lothar Hennighausen and Daniel Link: Csf3r mutations in mice confer a strong clonal HSC advantage via activation of Stat5. J Clin Invest 118, 946-955 (2008)
PMid:18292815    PMCid:2248325

12. M. William Lensch, R. Keaney Rathbun, Susan Olson, Gary Jones and Grover Bagby Jr: Selective pressure as an essential force in molecular evolution of myeloid leukemic clones: a view from the window of Fanconi anemia. Leukemia 13, 1784-1789 (1999)

13. Brian Druker, François Guilhot, Stephen O'Brien, Insa Gathmann, Hagop Kantarjian, Norbert Gattermann, Michael Deininger, Richard Silver, John Goldman, Richard Stone, Francisco Cervantes, Andreas Hochhaus, Bayard Powell, Janice Gabrilove, Philippe Rousselot, Josy Reiffers, Jan Cornelissen, Timothy Hughes, Hermine Agis, Thomas Fischer, Gregor Verhoef, John Shepherd, Giuseppe Saglio, Alois Gratwohl, Johan Nielsen, Jerald Radich, Bengt Simonsson, Kerry Taylor, Michele Baccarani, Charlene So, Laurie Letvak, and Richard Larson for the IRIS Investigators: Five-year follow-up of patients receiving imatinib for chronic myeloid leukemia. N Engl J Med 355, 2408-2417 (2006)

14. Brian Druker: Translation of the Philadelphia chromosome into therapy for CML. Blood 112, 4808-4817 (2008)

15. Jeffrey Tyner, Michael Deininger, Marc Loriaux, Bill Chang, Jason Gotlib, Stephanie Willis, Heidi Erickson, Tibor Kovacsovics, Thomas O'Hare, Michael Heinrich and Brian Druker: RNAi screen for rapid therapeutic target identification in leukemia patients. Proc Natl Acad Sci U S A 106, 8695-8700 (2009)
PMid:19433805    PMCid:2680429

16. Sheri Tinnell Dorsam, Christina Ferrell, Glenn Dorsam, Mika Kakefuda Derynck, Ulka Vijapurkar, Daniel Khodabakhsh, Bonnie Pau, Hillary Bernstein, Christopher Haqq, Corey Largman, and H. Jeffrey Lawrence: The transcriptome of the leukemogenic homeoprotein HOXA9 in human hematopoietic cells. Blood 103, 1676-1684 (2004)

17. Christian Bach, Sebastian Buhl, Dorothée Mueller, María-Paz García-Cuéllar, Emanuel Maethner, and Robert Slany: Leukemogenic transformation by HOXA cluster genes. Blood 115, 2910-2918 (2010)

18. Carolina Abramovich and R. Keith Humphries: Hox regulation of normal and leukemic hematopoietic stem cells. Curr Opin Hematol 12, 210-216 (2005)

19. Unnur Thorsteinsdottir, Aline Mamo, Evert Kroon, Lori Jerome, Janet Bijl, H. Jeffrey Lawrence, Keith Humphries and Guy Sauvageau: Overexpression of the myeloid leukemia-associated Hoxa9 gene in bone marrow cells induces stem cell expansion. Blood 99, 121-129 (2002)

20. Evert Kroon, Jana Krosl, Unnur Thorsteinsdottir, Soheyl Baban, Arthur Buchberg and Guy Sauvageau: Hoxa9 transforms primary bone marrow cells through specific collaboration with Meis1a but not Pbx1b. EMBO J 17, 3714-3725 (1998)
PMid:9649441    PMCid:1170707

21. Paul Ayton and Michael Cleary: Transformation of myeloid progenitors by MLL oncoproteins is dependent on Hoxa7 and Hoxa9. Genes Dev 17, 2298-2307 (2003)

22. Michael Milsom, Bernhard Schiedlmeier, Jeff Bailey, Mi-Ok Kim, Dandan Li, Michael Jansen, Abdullah Mahmood Ali, Michelle Kirby, Christopher Baum, Leslie Fairbairn and David Williams: Ectopic HOXB4 overcomes the inhibitory effect of tumor necrosis factor-alpha on Fanconi anemia hematopoietic stem and progenitor cells. Blood 113, 5111-5120 (2009)
PMid:19270262    PMCid:2686182

23. Joseph Wiemels, Zhijian Xiao, Patricia Buffler, Ana Maia, Xiaomei Ma, Brian Dicks, Martyn Smith, Luoping Zhang, James Feusner, John Wiencke, Kathy Pritchard-Jones, Helena Kempski, and Mel Greaves: In utero origin of t(8;21) AML1-ETO translocations in childhood acute myeloid leukemia. Blood 99, 3801-3805 (2002)

24. Hiroshi Mori, Susan Colman, Zhijian Xiao, Anthony Ford, Lyn Healy, Craig Donaldson, Jill Hows, Cristina Navarrete and Mel Greaves: Chromosome translocations and covert leukemic clones are generated during normal fetal development. Proc Natl Acad Sci USA 99, 8242-8247 (2002)
PMid:12048236    PMCid:123052

25. Dengli Hong, Rajeev Gupta, Philip Ancliff, Ann Atzberger, John Brown, Shamit Soneji, Joanne Green, Sue Colman, Wanda Piacibello, Veronica Buckle, Shinobu Tsuzuki, Mel Greaves and Tariq Enver: Initiating and cancer-propagating cells in TEL-AML1-associated childhood leukemia. Science 319, 336-339 (2008)

26. Robert Unckless and H. Allen Orr, The population genetics of adaptation: multiple substitutions on a smooth fitness landscape. Genetics 183, 1079-1086 (2009)
PMid:19737750    PMCid:2778961

27. Grover Bagby and Gabrielle Meyers: Myelodysplasia and acute leukemia as late complications of marrow failure: future prospects for leukemia prevention. Hematol Oncol Clin North Am 23, 361-376 (2009)
PMid:19327589    PMCid:2697169

28. Peter Lakatos and Lazlo Lakatos: Risk for colorectal cancer in ulcerative colitis: changes, causes and management strategies. World J Gastroenterol 14, 3937-3947 (2008)
PMid:18609676    PMCid:2725331

29. Robert Hammer, James Richardson, William Simmons, A. L. White, Maxime Breban, and Joel Taurog: High prevalence of colorectal cancer in HLA-B27 transgenic F344 rats with chronic inflammatory bowel disease. J Investig Med 43, 262-268 (1995)

30. Uwe Rudolph, Milton Finegold, Susan Rich, Gregory Harriman, Yogambal Srinivasan, Philippe Brabet, Guylain Boulay, Allan Bradley and Lutz Birnbaumer: Ulcerative colitis and adenocarcinoma of the colon in G alpha i2-deficient mice. Nat Genet 10, 143-150 (1995)

31. Boryana Popivanova, Kazuya Kitamura, Yu Wu, Toshikazu Kondo, Takashi Kagaya, Shiuchi Kaneko, Masanobu Oshima, Chifumi Fujii and Naofumi Mukaida: Blocking TNF-alpha in mice reduces colorectal carcinogenesis associated with chronic colitis. J Clin Invest 118, 560-570 (2008)
PMid:18219394    PMCid:2213370

32. Yoshitaka Kamegaya, Yiochi Hiasa, Lawrence Zukerberg, Nina Fowler, Jason Blackard, Wenyu Lin, Won Choe, Emmett Schmidt and Raymond Chung: Hepatitis C virus acts as a tumor accelerator by blocking apoptosis in a mouse model of hepatocarcinogenesis. Hepatology 41, 660-667 (2005)

33. Heike Bantel and Klaus Schulze-Osthoff: Apoptosis in hepatitis C virus infection. Cell Death Differ 10, S48-S58 (2003)

34. Katerina Dvorakova, Claire Payne, Lois Ramsey, Harris Bernstein, Hana Holubec, Melissa Chavarria, Carol Bernstein, Richard Sampliner, Catherine Riley, Anil Prasad and Harinder Garewal: Apoptosis resistance in Barrett's esophagus: Ex vivo bioassay of live stressed tissues. American Journal of Gastroenterology 100, 424-431 (2005)

35. Tohru Niwa, Tetsuya Tsukamoto, Takeshi Toyoda, Akiko Mori, Harunari Tanaka, Takao Maekita, Masao Ichinose, Masae Tatematsu and Toshikazu Ushijima: Inflammatory Processes Triggered by Helicobacter pylori Infection Cause Aberrant DNA Methylation in Gastric Epithelial Cells. Cancer Res 70, 1430-1440 (2010)

36. Alberto Mantovani: Cancer: Inflaming metastasis. Nature 457, 36-37 (2009)

37. Omar Sharif, Viacheslav Bolshakov, Stephanie Raines, Peter Newham and Neil Perkin: Transcriptional profiling of the LPS induced NF-kappaB response in macrophages. BMC Immunol 8, 1 (2007)
PMid:17222336    PMCid:1781469

38. Florian Greten, Lars Eckmann, Tim Greten, Jin Mo Park, Zhi-Wei Li, Laurence Egan, Martin Kagnoff and Michael Karin: IKKbeta links inflammation and tumorigenesis in a mouse model of colitis-associated cancer. Cell 118, 285-296 (2004)

39. Jun-Li Luo, Shin Maeda, Li-Chung Hsu, Hideo Yagita and Michael Karin: Inhibition of NF-kappaB in cancer cells converts inflammation- induced tumor growth mediated by TNFalpha to TRAIL-mediated tumor regression. Cancer Cell 6, 297-305 (2004)
PMid:9539021    PMCid:1533298

40. James Klaunig, Yong Xu, Jason Isenberg, Stephen Bachowski, Kyle Kolaja, Jiazhong Jiang, Donald Stevenson and Earl Walborg: The role of oxidative stress in chemical carcinogenesis. Environ Health Perspect 106, 289-295 (1998)
PMid:18978338    PMCid:2639036

41. Scott Maynard, Shepherd Schurman, Charlotte Harboe, Nadja de Souza-Pinto and Vilhelm Bohr: Base excision repair of oxidative DNA damage and association with cancer and aging. Carcinogenesis 30, 2-10 (2009).

42. Kaori Ishikawa, Keizo Takenaga, Miho Akimoto, Nobuko Koshikawa, Aya Yamaguchi, Hirotake Imanishi, Kazuto Nakada, Yoshio Honma, Jun-Ichi Hayashi: ROS-generating mitochondrial DNA mutations can regulate tumor cell metastasis. Science 320, 661-664 (2008).
PMid:19242562    PMCid:2647842

43. M. A. Joyce, K. A. Walters, S. E. Lamb, M. M. Yeh, L. F. Zhu, N. Kneteman, J. S. Doyle, M. G. Katze and D. L. Tyrrell, HCV induces oxidative and ER stress, and sensitizes infected cells to apoptosis in SCID/Alb-uPA mice. PLoS Pathog 5, e1000291 (2009).

44. Jakob Seidelin and Ole Nielsen: Attenuated apoptosis response to Fas-ligand in active ulcerative colitis. Inflamm Bowel Dis 14, 1623-1629 (2008)

45. H. Allen Orr: The population genetics of beneficial mutations. Philos Trans R Soc Lond B Biol Sci 365, 1195-1201 (2010)

46. Michael Nachman, Hopi Hoekstra and Susan D'Agostino: The genetic basis of adaptive melanism in pocket mice. Proc Natl Acad Sci U S A 100, 5268-5273 (2003)
PMid:12704245    PMCid:154334

47. Michael Majerus and Nicholas Mundy: Mammalian melanism: natural selection in black and white. Trends Genet 19, 585-588 (2003)

48. H. Allen Orr: Fitness and its role in evolutionary genetics. Nat Rev Genet 10, 531-539 (2009)
PMid:19546856    PMCid:2753274

49. Ivana Bjedov, Olivier Tenaillon, Bénédicte Gérard,Valeria Souza, Erick Denamur, Miroslav Radman, François Taddei and Ivan Matic: Stress-induced mutagenesis in bacteria. Science 300, 1404-1409 (2003).

50. Patricia Foster, Stress responses and genetic variation in bacteria. Mutat Res 569, 3-11 (2005).
PMid:15603749    PMCid:2729700

51. Alexander Anderson, AlissaWeaver, Peter Cummings and Vito Quaranta: Tumor morphology and phenotypic evolution driven by selective pressure from the microenvironment. Cell 127, 905-915 (2006)
PMid:16778145    PMCid:1895575

52. Neal Young, Rodrigo Calado and Phillip Scheinberg: Current concepts in the pathophysiology and treatment of aplastic anemia. Blood 108, 2509-2519 (2006)

53. Antonio Risitano, Jaroslaw Maciejewski, Spencer Green, Magdalena Plasilova, Weihua Zeng and Neal Young: In-vivo dominant immune responses in aplastic anaemia: molecular tracking of putatively pathogenetic T-cell clones by TCR beta-CDR3 sequencing. LANCET 364, 355-364 (2004)

54. Elaine Sloand, Sonnie Kim, Jaroslaw Maciejewski, John Tisdale, Dean Follmann, and Neal Young: Intracellular interferon-gamma in circulating and marrow T cells detected by flow cytometry and the response to immunosuppressive therapy in patients with aplastic anemia. Blood 100, 1185-1191 (2002)

55. Michael Bloom, Adam Wolk, Karen Simon-Stoos, Julie Bard, Jichun Chen and Neal Young: A mouse model of lymphocyte infusion-induced bone marrow failure. Exp Hematol 32, 1163-1172 (2004).

56. Weihua Zeng, Sachiko Kajigaya, Guibin Chen, Antonio Risitano, Olga Nunez and Neal Young: Transcript profile of CD4+ and CD8+ T cells from the bone marrow of acquired aplastic anemia patients. Exp Hematol 32, 806-814 (2004)

57. Weihua Zeng, Guibin Chen, Sachiko Kajigaya, Olga Nunez, Alexandra Charrow, Eric Billings and Neal Young: Gene expression profiling in CD34 cells to identify differences between aplastic anemia patients and healthy volunteers. Blood 103, 325-332 (2004)

58. Johan de Winter and Hans Joenje: The genetic and molecular basis of Fanconi anemia. Mutat Res 668, 11-19 (2009)

59. Grover Bagby and Blanche Alter: Fanconi anemia. Semin Hematol 43, 147-156 (2006)

60. Grover Bagby: Genetic basis of Fanconi anemia. Curr Opin Hematol 10, 68-76 (2003)

61. Fiona Vaz, Helmut Hanenberg, Beatrice Schuster, Karen Barker, Constanze Wiek, Verena Erven, Kornelia Neveling, Daniela Endt, Ian Kesterton, Flavia Autore, Franca Fraternali, Marcel Freund, Linda Hartmann, David Grimwade, Roland Roberts, Heiner Schaal, Shehla Mohammed, Nazneen Rahman, Detlev Schindler and Christopher Mathew: Mutation of the RAD51C gene in a Fanconi anemia-like disorder. Nat Genet 42, 406-409 (2010)

62. Arleen Auerbach, Barbara Adler and R. S. Chaganti: Prenatal and postnatal diagnosis and carrier detection of Fanconi anemia by a cytogenetic method. Pediatrics 67, 128-135 (1981)

63. Guido Fanconi: Familiare infantile perniziosaartige anaemia (pernizioses blutbild und konstitution). Jahrb Kinderhilkd 117, 257-280 (1927)

64. Grover Bagby and Gabrielle Meyers: Bone Marrow Failure as a Risk Factor for Clonal Evolution: Prospects for Leukemia Prevention. Hematology 2007, 40-46 (2007)

65. Phillip Rosenberg, Mark Greene and Blanche Alter, Cancer incidence in persons with Fanconi anemia. Blood 101, 822-826 (2003)

66. Qishen Pang, Tracy Christianson, Winifred Keeble, Jane Diaz, Gregory Faulkner, Carol Reifsteck, Susan Olson, and Grover Bagby: The Fanconi anemia complementation group C gene product: structural evidence of multifunctionality. Blood 98, 1392-1401 (2001)

67. Laura Hays, Winifred Keeble, Jane Yates, R. Keaney Rathbun, Tara Koretsky, Susan Olson, Zejin Sun, D. Wade Clapp, and Grover Bagby: Human FANCC is hypomorphic in murine Fancc-deficient cells. Blood (2010)(Epub ahead of print)

68. Carlo Dufour, Anna Corcione, Johanna Svahn, Riccardo Haupt, Nicoletta Battilana, and Vito Pistoia: Interferon gamma and tumour necrosis factor alpha are overexpressed in bone marrow T lymphocytes from paediatric patients with aplastic anaemia. Br J Haematol 115, 1023-1031 (2001)

69. Carlo Dufour, Anna Corcione, Johanna Svahn, Riccardo Haupt, Vincenzo Poggi, Albert Nandor Béka'ssy, Rosanna Scimè, Angela Pistorio, and Vito Pistoia: TNF-α and IFN-γ are over expressed in the bone marrow of Fanconi anemia patients and TNF-α suppresses erythropoiesis in vitro. Blood 102, 2053-2059 (2003)

70. Scott Vanderwerf, Johanna Svahn, Susan Olson, R. Keaney Rathbun, Christina Harrington, Jane Yates, Winifred Keeble, David Anderson, Praveen Anur, Noemi Pereira, Daniela Pilonetto, Ricardo Pasquini, and Grover Bagby: TLR8-dependent TNFα overexpression in Fanconi anemia group C cells. Blood 114, 5290-5298 (2009)
PMid:11500375    PMCid:125562

71. Qishen Pang, Winifred Keeble, Tracy Christianson, Gregory Faulkner, and Grover Bagby: FANCC interacts with hsp70 to protect hematopoietic cells from IFNγ/TNFα- mediated cytotoxicity. EMBO J 20, 4478-4489 (2001)

72. Paul Koh, Grant Hughes, Gregory Faulkner, Winifred Keeble and Grover Bagby: The Fanconi anemia group C gene product modulates apoptotic responses to tumor necrosis factor-a and Fas ligand but does not suppress expression of receptors of the tumor necrosis factor receptor superfamily. Exp Hematol 27, 1-8 (1999)

73. Michael Whitney, Gordon Royle, Michelle Low, Michelle Kelly, Michael Axthelm, Carol Reifsteck, Susan Olson, Robert Braun, Michael Heinrich, R. Keaney Rathbun, Grover Bagby and Markus Grompe: Germ cell defects and hematopoietic hypersensitivity to g-interferon in mice with a targeted disruption of the Fanconi anemia C gene. Blood 88, 49-58 (1996)

74. Laura Haneline, Hal Broxmeyer, Scott Cooper, Giao Hangoc, Madeleine Carreau, Manuel Buchwald and D. Wade Clapp: Multiple inhibitory cytokines induce deregulated progenitor growth and apoptosis in hematopoietic cells from FAC-/- mice. Blood 91, 4092-4098 (1998)

75. Simona Pigullo1, Elisa Ferretti2, Marina Lanciotti, Maurizio Bruschi, Giovanni Candiano, Johanna Svahn, Laura Haneline, Carlo Dufour, Vito Pistoia, Anna Corcione: Human Fanconi A cells are susceptible to TRAIL-induced apoptosis. Br J Haematol 136, 315-318 (2007)
PMid:16946306    PMCid:1895443

76. Yue Si, Samantha Ciccone, Feng-Chun Yang, Jin Yuan, Daisy Zeng, Shi Chen, Henri van de Vrugt, John Critser, Fre Arwert, Laura Haneline, and D. Wade Clapp: Continuous in vivo infusion of interferon-gamma enhances engraftment of syngeneic wild-type cells in Fanca-/- and Fancg-/- mice. Blood 108, 4283-4287 (2006)

77. Xiaxin Li, Yanzhu Yang, Jin Yuan, Ping Hong, Brian Freie, Attilio Orazi, Laura Haneline, and D. Wade Clapp: Continuous in vivo infusion of interferon-gamma (IFN-γ) preferentially reduces myeloid progenitor numbers and enhances engraftment of syngeneic wildtype cells in Fancc-/- mice. Blood 104, 1209 (2004)
PMid:17404312    PMCid:2919363

78. Daniel Sejas, Reena Rani, Yuhui Qiu, Xiaoling Zhang, Sara Fagerlie, Hiroyasu Nakano, David Williams, and Qishen Pang: Inflammatory reactive oxygen species-mediated hemopoietic suppression in Fancc-deficient mice. J Immunol 178, 5277-5287 (2007)
PMid:17405815    PMCid:2857731

79. Xiaoling Zhang, Daniel Sejas,Yuhui Qiu, David Williams, and Qishen Pang: Inflammatory ROS promote and cooperate with the Fanconi anemia mutation for hematopoietic senescence. J Cell Sci 120, 1572-1583 (2007)

80. Qishen Pang, Winifred Keeble, Jane Diaz, Tracy Christianson, Sara Fagerlie, Keaney Rathbun, Gregory Faulkner, Michael O'Dwyer, and Grover Bagby: Role of double-stranded RNA-dependent protein kinase in mediating hypersensitivity of Fanconi anemia complementation group C cells to interferon gamma, tumor necrosis factor-alpha, and double-stranded RNA. Blood 97, 1644-1652 (2001)

81. R. Keaney Rathbun, Tracy Christianson, Gregory Faulkner, Gary Jones, Winifred Keeble, Michael O'Dwyer, and Grover Bagby: Interferon-g-induced apoptotic responses of Fanconi anemia group C hematopoietic progenitor cells involve caspase 8-dependent activation of caspase 3 family members. Blood 96, 4204-4211 (2000)

82. Xiaoling Zhang, June Li, Daniel Sejas, Keaney Rathbun, Grover Bagby, and Qishen Pang: The Fanconi anemia proteins functionally interact with the protein kinase regulated by RNA (PKR). J Biol Chem 279, 43910-43919 (2004)
PMid:16109778    PMCid:1895245

83. Khadijeh Bijangi-Vishehsaraei, M. Reza Saadatzadeh, Adam Werne, Kristina Wilson McKenzie, Reuben Kapur, Hidenori Ichijo, and Laura Haneline: Enhanced TNF-α-induced apoptosis in Fanconi anemia type C-deficient cells is dependent on apoptosis signal-regulating kinase 1. Blood 106, 4124-4130 (2005)

84. Qishen Pang, Tracy Christianson, Winifred Keeble, Tara Koretsky and Grover Bagby: The anti-apoptotic function of Hsp70 in the interferon-inducible double-stranded RNA-dependent protein kinase-mediated death signaling pathway requires the Fanconi anemia protein, FANCC. Journal of Biological Chemistry 277, 49638-49643 (2002)

85. John Schultz and Nasrollah Shahidi: Tumor necrosis factor-alpha overproduction in Fanconi's anemia. Am J Hematol 42, 196-201 (1993)

86. Asmin Tulpule, M. William Lensch, Justine Miller, Karyn Austin, Alan D'Andrea, Thorsten M. Schlaeger, Akiko Shimamura, and George Q. Daley: Knockdown of Fanconi anemia genes in human embryonic stem cells reveals early developmental defects in the hematopoietic lineage. Blood 115, 3453-3462 (2010)

87. Eva Guinan: Acquired aplastic anemia in childhood. Hematol Oncol Clin North Am 23, 171-191 (2009)

88. Yigal Dror and Melvin Freedman: Shwachman-Diamond syndrome marrow cells show abnormally increased apoptosis mediated through the Fas pathway. Blood 97, 3011-3016 (2001)

89. Inga Köllner, Beate Sodeik, Sabine Schreek, Holger Heyn,Nils von Neuhoff, Manuela Germeshausen, Cornelia Zeidler, Martin Krüger, Brigitte Schlegelberger, Karl Welte, and Carmela Beger: Mutations in neutrophil elastase causing congenital neutropenia lead to cytoplasmic protein accumulation and induction of the unfolded protein response. Blood 108, 493-500 (2006)

90. Andrew Yoon, Guang Peng, Yves Brandenburg, Ornella Zollo, Wei Xu, Eduardo Rego, and Davide Ruggero: Impaired control of IRES-mediated translation in X-linked dyskeratosis congenita. Science 312, 902-906 (2006)

91. Michaela Gross, Helmut Hanenberg, Stephan Lobitz, Richard Friedl, Sabine Herterich, Ralf Dietrich, Bernd Gruhn, Detlev Schindler and Holger Hoehn: Reverse mosaicism in Fanconi anemia: natural gene therapy via molecular self-correction. Cytogenet Cell Genet 98, 126-135 (2002)

92. John Gregory, Jr., John Wagner, Peter Verlander, Orna Levran, Sat Dev Batish, Cindy Eide, Amy Steffenhagen, Betsy Hirsch, Arleen Auerbach: Somatic mosaicism in Fanconi anemia: evidence of genotypic reversion in lymphohematopoietic stem cells. Proc Natl Acad Sci U S A 98, 2532-2537 (2001)
PMid:11226273    PMCid:30172

93. Quinten Waisfisz, Neil Morgan, Maria Savino, Johan de Winter, Carola van Berkel, Maureen Hoatlin, Leonarda Ianzano, Rachel Gibson, Fre Arwert, Anna Savoia, Christopher Mathew, Jan Pronk, and Hans Joenje: Spontaneous functional correction of homozygous Fanconi anaemia alleles reveals novel mechanistic basis for reverse mosaicism. Nat Genet 22, 379-383 (1999)

94. Anuj Mankad, Toshiyasu Taniguchi, Barbara Cox, Yassmine Akkari, R. Keaney Rathbun, Lora Lucas, Grover Bagby, Susan Olson, Alan D'Andrea, and Markus Grompe: Natural gene therapy in monozygotic twins with Fanconi anemia. Blood 107, 3084-3090 (2006)
PMid:16397136    PMCid:1895746

95. Brian Freie, Xiaxin Li, Samantha Ciccone, Kathy Nawa, Scott Cooper, Catherine Vogelweid, Laurel Schantz, Laura Haneline, Attilio Orazi, Hal Broxmeyer, Suk-Hee Lee, and D. Wade Clapp: Fanconi anemia type C and p53 cooperate in apoptosis and tumorigenesis. Blood 102, 4146-4152 (2003)

96. Xiaxin Li, Michelle Le Beau, Samantha Ciccone, Feng-Chun Yang, Brian Freie, Shi Chen, Jin Yuan, Ping Hong,Attilio Orazi, Laura Haneline, and D. Wade Clapp: Ex vivo culture of Fancc-/- stem/progenitor cells predisposes cells to undergo apoptosis, and surviving stem/progenitor cells display cytogenetic abnormalities and an increased risk of malignancy. Blood 105, 3465-3471 (2005)
PMid:15644418    PMCid:1895016

97. Laura Haneline, Xiaxin Li, Samantha Ciccone, Ping Hong, Yanzhu Yang, Hal Broxmeyer, Suk-Hee Lee, Attilio Orazi, Edward Srour, and D. Wade Clapp: Retroviral-mediated expression of recombinant Fancc enhances the repopulating ability of Fancc-/- hematopoietic stem cells and decreases the risk of clonal evolution. Blood 101, 1299-1307 (2003)

98. Pachiyappan Kamarajan, Nian-Kang Sun and Chuck C.-K. Chao: Up-regulation of FLIP in cisplatin-selected HeLa cells causes cross-resistance to CD95/Fas death signalling. Biochem J 376, 253-260 (2003)
PMid:12911332    PMCid:1223749

99. Shenghao Jin, Huiwu Zhao, Yan Yi, Yuji Nakata, Anna Kalota, and Alan Gewirtz: c-Myb binds MLL through menin in human leukemia cells and is an important driver of MLL-associated leukemogenesis. J Clin Invest 120, 593-606 (2010)
PMid:20093773    PMCid:2810070

100. Francesco Fazi, Serena Racanicchi, Giuseppe Zardo, Linda Starnes, Marco Mancini, Lorena Travaglini, Daniela Diverio, Emanuele Ammatuna, Giuseppe Cimino,Francesco Lo-Coco, Francesco Grignani, and Clara Nervi: Epigenetic silencing of the myelopoiesis regulator microRNA-223 by the AML1/ETO oncoprotein. Cancer Cell 12, 457-466 (2007)

101. Paul Ayton, Everett Chen, and Michael Cleary: Binding to nonmethylated CpG DNA is essential for target recognition, transactivation, and myeloid transformation by an MLL oncoprotein. Mol Cell Biol 24, 10470-10478 (2004)
PMid:15542854    PMCid:529055

102. Maria Figueroa, Bas Wouters, Lucy Skrabanek, Jacob Glass, Yushan Li, Claudia Erpelinck-Verschueren, Anton Langerak, Bob Löwenberg, Melissa Fazzari, John Greally, Peter Valk, Ari Melnick, and Ruud Delwel: Genome-wide epigenetic analysis delineates a biologically distinct immature acute leukemia with myeloid/T-lymphoid features. Blood 113, 2795-2804 (2009)

103. Ting Xi Liu, Michael Becker, Jaroslav Jelinek, Wen-Shu Wu, Min Deng, Natallia Mikhalkevich, Karl Hsu, Clara Bloomfield, Richard Stone, Daniel DeAngelo, Ilene Galinsky, Jean-Pierre Issa, Michael Clarke, and A Thomas Look: Chromosome 5q deletion and epigenetic suppression of the gene encoding alpha-catenin (CTNNA1) in myeloid cell transformation. Nat Med 13, 78-83 (2007)

104. Joanna Baxter, Linda M Scott, Peter J Campbell, Clare East, Nasios Fourouclas, Soheila Swanton, George S Vassiliou, Anthony J Bench, Elaine M Boyd, Natasha Curti, Mike A Scott, Wendy N Erber, and Anthony R Green, Acquired mutation of the tyrosine kinase JAK2 in human myeloproliferative disorders. LANCET 365, 1054-1061 (2005)

105. Chloé James, Valérie Ugo, Jean-Pierre Le Couédic, Judith Staerk, François Delhommeau, Catherine Lacout, Loïc Garçon, Hana Raslova, Roland Berger, Annelise Bennaceur-Griscelli, Jean Luc Villeval, Stefan Constantinescu, Nicole Casadevall, and William Vainchenker: A unique clonal JAK2 mutation leading to constitutive signalling causes polycythaemia vera. Nature 434, 1144-1148 (2005)

106. Robert Kralovics, Francesco Passamonti, Andreas Buser, Soon-Siong Teo, Ralph Tiedt, Jakob Passweg, Andre Tichelli, Mario Cazzola, and Radek Skoda: A gain-of-function mutation of JAK2 in myeloproliferative disorders. N Engl J Med 352, 1779-1790 (2005)

107. Ross Levine, Martha Wadleigh, Jan Cools, Benjamin Ebert, Gerlinde Wernig, Brian Huntly, Titus Boggon, Iwona Wlodarska, Jennifer Clark, Sandra Moore, Jennifer Adelsperger, Sumin Koo, Jeffrey Lee, Stacey Gabriel, Thomas Mercher, Alan D'Andrea, Stefan Fröhling, Konstanze Döhner, Peter Marynen, Peter Vandenberghe, Ruben Mesa, Ayalew Tefferi, James Griffin, Michael Eck, William Sellers, Matthew Meyerson, Todd Golub, Stephanie Lee, and D. Gary Gilliland: Activating mutation in the tyrosine kinase JAK2 in polycythemia vera, essential thrombocythemia, and myeloid metaplasia with myelofibrosis. Cancer Cell 7, 387-397 (2005)

108. Runxiang Zhao, Shu Xing, Zhe Li, Xueqi Fu, Qingshan Li, Sanford Krantz, and Zhizhuang Joe Zhao: Identification of an acquired JAK2 mutation in polycythemia vera. J Biol Chem 280, 22788-22792 (2005)
PMid:15863514    PMCid:1201515

109. Catriona Jamieson, Jason Gotlib, Jeffrey Durocher, Mark Chao, M. Rajan Mariappan, Marla Lay, Carol Jones, James Zehnder, Stan Lilleberg, and Irving Weissman: The JAK2 V617F mutation occurs in hematopoietic stem cells in polycythemia vera and predisposes toward erythroid differentiation. Proc Natl Acad Sci U S A 103, 6224-6229 (2006)
PMid:16603627    PMCid:1434515

110. Thomas Bumm, Collin Elsea, Amie Corbin, Marc Loriaux, Daniel Sherbenou, Lisa Wood, Jutta Deininger, Richard Silver, Brian Druker, and Michael Deininger: Characterization of murine JAK2V617F-positive myeloproliferative disease. Cancer Res 66, 11156-11165 (2006)

111. Catherine Lacout, Didier Pisani, Micheline Tulliez, Françoise Moreau Gachelin, William Vainchenker, and Jean-Luc Villeval: JAK2V617F expression in murine hematopoietic cells leads to MPD mimicking human PV with secondary myelofibrosis. Blood 108, 1652-1660 (2006)

112. Gerlinde Wernig, Thomas Mercher, Rachel Okabe, Ross Levine, Benjamin Lee, and D. Gary Gilliland: Expression of Jak2V617F causes a polycythemia vera-like disease with associated myelofibrosis in a murine bone marrow transplant model. Blood 107, 4274-4281 (2006)
PMid:16478879    PMCid:1895786

113. Ralph Tiedt, Hui Hao-Shen, Marta Sobas, Renate Looser, Stephan Dirnhofer, Jürg Schwaller, and Radek Skoda: Ratio of mutant JAK2-V617F to wild-type Jak2 determines the MPD phenotypes in transgenic mice. Blood 111, 3931-3940 (2008)

114. Hajime Akada, Dongqing Yan, Haiying Zou, Steven Fiering, Robert Hutchison, and M. Golam Mohi: Conditional expression of heterozygous or homozygous Jak2V617F from its endogenous promoter induces a polycythemia vera-like disease. Blood 115, 3589-3597 (2010)

115. Juan Li, Dominik Spensberger, Jong Sook Ahn, Shubha Anand, Philip Beer, Cedric Ghevaert, Edwin Chen, Ariel Forrai, Linda Scott, Rita Ferreira, Peter Campbell, Steve Watson, Pentao Liu, Wendy Erber, Brian Huntly, Katrin Ottersbach, and Anthony Green: JAK2 V617F impairs hematopoietic stem cell function in a conditional knock-in mouse model of JAK2 V617F-positive essential thrombocythemia. Blood (2010) (Epub ahead of print)

116. Ann Mullally, Steven Lane, Brian Ball, Christine Megerdichian, Rachel Okabe, Fatima Al-Shahrour, Mahnaz Paktinat, J. Erika Haydu, Elizabeth Housman, Allegra Lord, Gerlinde Wernig, Michael Kharas, Thomas Mercher, Jeffery Kutok, D. Gary Gilliland, and Benjamin Ebert: Physiological Jak2V617F expression causes a lethal myeloproliferative neoplasm with differential effects on hematopoietic stem and progenitor cells. Cancer Cell 17, 584-596 (2010)

117. Kalindi Parmar, Alan D'Andrea, and Laura Niedernhofer: Mouse models of Fanconi anemia. Mutat Res 668, 133-140 (2009)
PMid:19427003    PMCid:2778466

118. Ming Zhang, Jun Qian, Xianying Xing, Feng-Ming Kong, Lujun Zhao, Ming Chenand Theodore Lawrence: Inhibition of the tumor necrosis factor-alpha pathway is radioprotective for the lung. Clin Cancer Res 14, 1868-1876 (2008)

119. Elisa Rumi: Familial chronic myeloproliferative disorders: the state of the art. Hematol Oncol 26, 131-138 (2008)

120. Outi Kilpivaara, Semanti Mukherjee, Alison Schram, Martha Wadleigh, Ann Mullally, Benjamin Ebert, Adam Bass, Sachie Marubayashi, Adriana Heguy, Guillermo Garcia-Manero, Hagop Kantarjian, Kenneth Offit, Richard Stone, D Gary Gilliland, Robert Klein, and Ross Levine: A germline JAK2 SNP is associated with predisposition to the development of JAK2(V617F)-positive myeloproliferative neoplasms. Nat Genet 41, 455-459 (2009)

121. Damla Olcaydu, Ashot Harutyunyan, Roland Jäger, Tiina Berg, Bettina Gisslinger, Ingrid Pabinger, Heinz Gisslinger, and Robert Kralovics: A common JAK2 haplotype confers susceptibility to myeloproliferative neoplasms. Nat Genet 41, 450-454 (2009)

122. Amy Jones, Andrew Chase, Richard Silver, David Oscier, Katerina Zoi, Y Lynn Wang, Holger Cario, Heike Pahl, Andrew Collins, Andreas Reite, Francis Grand, and Nicholas Cross: JAK2 haplotype is a major risk factor for the development of myeloproliferative neoplasms. Nat Genet 41, 446-449 (2009)

123. Dean Felsher: Tumor dormancy and oncogene addiction. APMIS 116, 629-637 (2008)

124. Jos Jonkers and Anton Berns: Oncogene addiction: sometimes a temporary slavery. Cancer Cell 6, 535-538 (2004)

125. Paul Workman: Cancer genome targets: RAF-ing up tumor cells to overcome oncogene addiction. Expert Rev Anticancer Ther 2, 611-614 (2002)

126. Jennifer Clark, Jan Cools, David Curley, Jin-Chen Yu, Nathalie Lokker, Neill A. Giese, and D. Gary Gilliland: Variable sensitivity of FLT3 activation loop mutations to the small molecule tyrosine kinase inhibitor MLN518. Blood 104, 2867-2872 (2004)

127. Ellen Weisberg, Christina Boulton, Louise Kelly, Paul Manley, Doriano Fabbro, Thomas Meyer, D. Gary Gilliland, and James Griffin: Inhibition of mutant FLT3 receptors in leukemia cells by the small molecule tyrosine kinase inhibitor PKC412. Cancer Cell 1, 433-443 (2002)

128. Stefan Fröhling, Claudia Scholl, Ross Levine, Marc Loriaux, Titus Boggon, Olivier Bernard, Roland Berger, Hartmut Döhner, Konstanze Döhner, Benjamin Ebert, Sewit Teckie, Todd Golub, Jingrui Jiang, Marcus Schittenhelm, Benjamin Lee, James Griffin, Richard Stone, Michael Heinrich, Michael Deininger, Brian Druker, and D. Gary Gilliland: Identification of driver and passenger mutations of FLT3 by high-throughput DNA sequence analysis and functional assessment of candidate alleles. Cancer Cell 12, 501-513 (2007)

129. Paul Wan, Mathew Garnett, S. Mark Roe, Sharlene Lee, Dan Niculescu-Duvaz, Valerie Good, C. Michael Jones, Christopher Marshall, Caroline Springer, David Barford, and Richard Marais: Mechanism of activation of the RAF-ERK signaling pathway by oncogenic mutations of B-RAF. Cell 116, 855-867 (2004)

Abbreviations: LPS- Bacterial Endotoxin, TNFa- Tumor necrosis factor alpha, IFNg - Interferon gamma, SCF - Stem cell factor (Steel factor), JAK - Janus kinase, STAT - signal transducer and activator of transcription, CFU-GM - Colony forming unit- granulocyte/macrophage, BFU-E - Burst forming unit, erythroid, IL-11 - Interleukin eleven, Flt3 - fms-related tyrosine kinase 3, Flt3L - Flt3 ligand, HOXA9 - Homeobox A9, HSC - Hematopoietic stem cell, SNP - Single nucleotide polymorphism, TLR - Toll-like receptor

Key Words: Leukemogenesis, Aplastic Anemia, Fanconi Anemia, Myeloproliferative Diseases, Tumor-Necrosis Factor-Alpha, Interferon-Gamma, Mutation, Clonal Evolution, Hematopoietic Stem Cells, review

Send correspondence to: Grover C. Bagby, NW VA Cancer Research Center; R&D, B103, E221B; Portland VA Medical Center, 3710 SW VA Hospital Road, Portland, Oregon 97239, Tel: 503-273-5008, Fax 503-721-7946, E-mail:grover@ohsu.edu