Definition Malignant melanoma is a type of cancer arising from the melanocyte cells of the skin. The melanocytes are cells in the skin that produce the pigment melanin. Malignant melanoma develops when the melanocytes no longer respond to normal control mechanisms of cellular growth and are capable of invasion locally or spread to other organs in the body (metastasis), where again they invade and compromise the function of that organ. Description Melanocytes, embryologically derived from the neural crest, are distributed in the epidermis and thus are found throughout the skin. They produce a brown pigment known as melanin and are responsible for racial variation in skin color and also the color of moles. Malignant degeneration of the melanocyte gives rise to the tumor, melanoma, of which there are four subtypes. These are: superficial spreading, nodular, lentigo maligna, and acral lentiginous melanomas, accounting for 70%, 15% to 30%, 4% to 10%, and 2% to 8% of cases, respectively. Malignant melanoma may develop anywhere on the body. In men, it is most common on the trunk. In women, it is most common on the back or legs. The subtype also may influence where the tumor develops, lentigo melanoma is more common on the face while acral lentiginous melanoma is more common on the palms of the hand, soles of the feet, or in the nail beds. The locally invasive characteristic of this tumor involves vertical penetration through the skin and into the dermis and subcutaneous (under-the-skin) tissues of the malignant melanocytes. With the exception of the nodular variety of melanoma, there is often a phase of radial or lateral growth associated with these tumors. Since it is the vertical growth that characterizes the malignancy, th... ...r, et al. "NRAS and BRAF Mutations Arise Early During Melanoma Pathogenesis and Are Preserved Throughout Tumor Progression." Clinical Cancer Research 9 (December 15, 2003): 6483â€“6488. Rockmann, H., and D. Schadendorf. "Drug Resistance in Human Melanoma: Mechanisms and Therapeutic Opportunities" Onkologie 26 (December 2003): 581â€“587. Weinstock, Martin A. "Early Detection of Melanoma." JAMA, The Journal of the American Medical Association 284 (16 August 2000): 886. Whiteman, D. C., P. Watt, D. M. Purdie, et al. "Melanocytic Nevi, Solar Keratoses, and Divergent Pathways to Cutaneous Melanoma." Journal of the National Cancer Institute 95 (June 4, 2003): 806â€“812. Other Cancer Resource Center American Cancer Society. [cited June 20, 2005]. . Melanoma Patient's Information Page. [cited June 20, 2005]. . National Cancer Institute. [cited June 13, 2005]. .
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