Definition Malignant melanoma is a type of cancer that originates from melanocyte cells in the skin. Melanocytes are skin cells that produce the pigment melanin. Malignant melanoma develops when melanocytes no longer respond to normal cell growth control mechanisms and are able to locally invade or spread to other organs of the body (metastasis), where they again invade and compromise the function of that organ.DescriptionMelanocytes , of embryological derivation from the neural crest, are distributed in the epidermis and are therefore 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. The malignant degeneration of melanocytes gives rise to the tumor, melanoma, of which there are four subtypes. These are: superficial spreading, nodular, lentigo maligna, and acral lentiginosis melanomas, which account for 70%, 15% to 30%, 4% to 10%, and 2% to 8% of cases, respectively. Malignant melanoma can develop anywhere in the body. In men it is more common on the trunk. In women, it is more common on the back or legs. The subtype can also 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 hands, soles of the feet, or nail beds. The locally invasive characteristic of this tumor involves vertical penetration through the skin and into the dermis and subcutaneous tissues (under the skin) of malignant melanocytes. With the exception of the nodular variety of melanoma, these tumors often have a radial or lateral growth phase. Since it is the vertical growth that characterizes the neoplasm, th...... half of the study ......r, et al. “NRAS and BRAF mutations appear early during melanoma pathogenesis and are preserved during tumor progression.” Clinical Cancer Research 9 (15 December 2003): 6483–6488. Rockmann, H. and D. Schadendorf. “Drug Resistance in Human Melanoma: Mechanisms and Therapeutic Opportunities” Onkologie 26 (December 2003): 581–587. 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): 806–812. OtherCancer Resource Center American Cancer Society. [cited June 20, 2005]. .Information page for patients with melanoma. [cited June 20, 2005]. .National Cancer Institute. [cited June 13, 2005]. .