- 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 which 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; and mitotic figures tend to be numerous. Prognosis correlates with the depth of skin invasion. Melanomas frequently metastasize widely; regional lymph node s, skin, liver, lungs, and brain are likely to be involved. Intense, intermittent sun exposure, especially of fair-skinned children, increases the risk of m. later in life. SYN: malignant m.. [melano- + G. -oma, tumor]- acral lentiginous m. a form of malignant lentigo m. that occurs in palms, soles, and subungual areas.- amelanotic m. an anaplastic m. consisting of cells derived from melanocytes but not forming melanin.- Cloudman m. a transplantable m. that arose spontaneously in a mouse of DBA strain, and which grows and metastasizes in mice of related strains.- desmoplastic malignant m. (dez-mo-plas-mik) a m. with marked fibrosis surrounding atypical spindle-shaped melanocytes in the dermis, tending to invade widely around small nerves.- Harding-Passey m. a melanin-forming tumor that arose spontaneously in a non-inbred mouse, and that is transplantable to mice of many strains but does not ordinarily metastasize.- malignant m. in situ a m. limited to the epidermis and composed of nests of atypical melanocytes and scattered single cells extending into the upper epidermis; local excision is curative although the lesion, if untreated, may soon invade the dermis. Malignant lentigo may be considered a slowly progressive type of malignant m. in situ.- minimal deviation m. a malignant m. showing less cytologic atypia than is usual in m. cells that nevertheless demonstrate asymmetric expansile invasion of the dermis, or metastasis.- nodular m. primary cutaneous m. that presents as rapidly growing smoothly spheroid or ulcerated nodules in which tumor cells microscopically invade the dermis beneath all of the lateral epidermal margins of involvement.- subungual m. a m. beginning in the skin at the border of or beneath the nail, usually of acral lentiginous type (q.v.).- superficial spreading m. primary cutaneous m. characterized by intraepidermal growth extending laterally beyond the site of dermal invasion.
* * *1) a benign or malignant skin tumor containing dark pigment2) a tumor of high malignancy that starts in melanocytes of normal skin or moles and metastasizes rapidly and widely called also malignant melanoma, melanocarcinoma, melanoepithelioma, melanosarcoma
* * *n.a highly malignant tumour of melanin-forming cells, the melanocyte. Such tumours usually occur in the skin (excessive exposure to sunlight is a contributory factor) but are also found in the eye and the mucous membranes. They may contain melanin or be free of pigment (amelanotic melanomas). Spread of this cancer to other parts of the body, especially to the lymph nodes and liver, is common. In these cases melanin or its precursors (melanogens) may be excreted in the urine and the whole of the skin may be deeply pigmented. The prognosis is inversely related to the thickness of the tumour; almost all patients with tumours less than 0.76 mm survive following surgical excision.
* * *mel·a·no·ma (mel″ə-noґmə) [melan- + -oma] 1. a tumor arising from melanocytes of the skin or other organs. 2. malignant m. melanomatous adj
Medical dictionary. 2011.