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Malignant Melanoma of the Skin
Malignant melanomas occur most commonly in fair-skinned persons, often those who have a history of sun exposure. Individuals who have genetically-determined hypersensitivity to ultraviolet irradiation (e.g., as in xeroderma pigmentosum) have a substantial risk of developing these neoplasms. Melanomas may take origin in any skin site, including the palms, soles, and nail beds. Most commonly they arise de novo, but approximately 15% are derived from pre-existing melanocytic nevi, such as “giant hairy” congenital nevi. Rarely, melanomas originate in the mucous membranes of the oral cavity, nasopharynx, vagina, urethra, anal canal, esophagus, bronchi, and biliary tree. In approximately one-third of patients who present with disseminated metastatic disease, the primary site of disease may not be found despite extensive clinical evaluation, and may be presumed to have regressed spontaneously. Improved detection and management of “early” melanomas has significantly lessened the mortality over the past 20 years.
