melanoma

= malignant melanoma; n.

a highly malignant tumour of melanin-forming cells, the melanocytes. Such tumours usually occur in the skin (excessive exposure to sunlight is a contributory factor) – usually arising from a pre-existing mole or naevus – 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. Melanoma can be responsive to immunotherapy and is currently the subject of investigational treatments using melanoma vaccines; the response rate to conventional chemotherapy is poor.