FEATURES AND APPEARANCE OF VARIOUS TYPES OF MALIGNANT MELANOMAS Superficial Spreading (70%) Nodular (15%) Acral Lentiginous (10%) Lentigo Malignant melanoma (5%) Superficial Spreading melanoma is characterized by a radial growth much greater than a vertical growth. The lesion appears as a flat, slow growing tumor. This tumor has a good prognosis. Nodular Malignant melanoma appears as a raised berry-shaped nodule. This tumor is characterized by a rapid vertical growth phase, metastasizes widely, and carry an extremely poor prognosis. Acral Lentiginous malignant melanoma is a slow growing, flat tumor, which frequently covers large areas of skin. This tumor is commonly found on the palms, soles, mucous membranes and underneath the nail. The prognosis of this lesion resides between that of the nodular and superficial spreading types. Lentigo Maligno melanoma grows at an extremely slow pace and is normally seen as a black lesion in a background of brown color. This tumor has an excellent prognosis. IMMUNE ESCAPE IN MALIGNANT MELANOMA Malignant melanoma is one of the skin cancers that arises from melanocytes within the epidermis or mucous membranes. Malignant melanoma appears as lesions which range in color from brown to dark blue (table). Among the predisposing factors are light skin tone and red or blonde hair, excessive sun exposure, xeroderma pigmentosum, dysplastic nevus syndrome, and a family history or previous personal history of melanoma. Encounter of the Fas positive cells with Fas ligand (FasL) leads to apoptosis of these cells. Hahne et al, report in the Nov 22, 96 issue of Science that melanoma cells express FasL on their surfaces both in vivo and in vitro. Therefore, it was hypothesized that the tumor cells may escape from the attack by the effector cells of the immune system within the tumor microenvironment by virtue of expression of FasL+. Such protection may be afforded to the tumor cells by the apoptosis of the Fas+ cells after encounter with the FasL within the tumor infiltrate. Consitent with this hypothesis, injection of FasL+ malignant melanoma cells to mice led to formation of tumors in these mice. However, tumors failed to grow in the Fas-deficient/lpr mutant mice. Four out of 10 wild-type mice exhibited palpable tumors within 4 days of injection of mouse melanoma cells that expressed Fas mRNA and protein. On the other hand, only 1 out of 10 Fas-deficient/lpr mutant mice had a palpable tumor on day 4. By day 6, the tumors were palpable in all wild-type mice whereas only 5 Fas-deficient/lpr mutant mice had a palpable tumor. The findings suggest that tumor cells may escape the immune attack by virtue of expression of FasL. REFERENCE: M. Hahne, D. Rimoldi, M. Schröter, P. Romero, M. Schreier, L. E. French, P. Schneider, T. Bornand, A. Fontana, D. Lienard, J.-C. Cerottini, J. Tschopp: Melanoma cell expression of Fas(Apo-1/CD95) ligand: Implications for tumor immune escape. Science 274, 1363-1365, 1996 RESOURCES: Malignant Melanoma RAFT Research Cancer - Malignant Melanoma Multimeda in the Prevention of Malignant Melanoma Malignant melanoma: staging Malignant melanoma detection Genetics of Cutaneous Malignant Melanoma Electronic textbook of dermatology A Tutorial in Dermatologic Pathology; Dept. of Dermatology - University of Iowa College of Medicine Gallery of Superficial Spreading Malignant Melanoma Warning Signs of Malignant Melanoma Pitfalls in Histopathologic Diagnosis of Malignant Melanoma Malignant Melanoma-Check for the ABCD's of Melanoma Malignant Melanoma DATABASE LINKS: Melanoma