Definition: A malignant neoplasm, derived from cells that are capable of forming melanin, arising most commonly in the skin of any part of the body, or in the eye, and, rarely, in the mucous membranes of the genitalia, anus, oral cavity, or other sites; occurs mostly in adults and may originate de novo or from a pigmented nevus or lentigo maligna. In the early phases, the cutaneous form is characterized by proliferation of cells at the dermal-epidermal junction, that soon invade adjacent tissues. The cells vary in amount and pigmentation of cytoplasm; the nuclei are relatively large and frequently bizarre in shape, with prominent acidophilic nucleoli; mitotic figures tend to be numerous. Prognosis correlates with the depth of skin invasion. Melanomas frequently metastasize widely; regional lymph nodes, skin, liver, lungs, and brain are likely to be involved. Intense, intermittent sun exposure, especially of fair-skinned children, increases the risk of melanoma later in life.
Synonym(s): malignant melanoma
[melano- + G. -ōma, tumor]