Malignant melanomas arising in the mucosal epithelial lining of the respiratory tract, gastrointestinal and genitourinary tracts are very rare, with an annual incidence of .15% per 100,000 individuals. Major sites of the mucosal melanomas are the vulva and vagina (45%), the head and neck, and the nasal and oral cavity (43%). Mucosal melanomas are so rare that there are no large data bases compared to those for cutaneous melanoma; therefore, pathologic microstaging has not been possible, and the fine tuning of the prognosis that has been useful in cutaneous melanoma (Breslow thickness and Clark levels) has so far not been possible in mucosal melanoma.
Most melanomas are believed to develop de novo from melanocytes within normal skin or mucosa. Ultraviolet radiation has been implicated as a major causative factor in the development of MM. Several cutaneous melanocytic lesions with the ability to undergo malignant transformation have been identified as possible precursor lesions to MM.
Five cutaneous lesions have been identified which possess the potential to undergo malignant transformation into melanoma. The dysplastic melanocytic nevus is thought to be the most frequent precursor lesion to MM and accounts for about 20% of the cases of this malignancy. They occur in about 2% of white adults.
Asymmetry in shape - one-half unlike the other half
Border is irregular - edges irregularly scalloped
Color is mottled - haphazard display of colors; shades of brown, black, gray, red, and white
Diameter is usually large - greater than the tip of a pencil eraser (6 mm)
Elevation is almost always present - surface distortion is assessed by side-lighting. Melanoma in situ and acral lentiginous lesions may be flat
Enlargement - a history of an increse in the size of lesion is perhaps one of the most important signs of malignant melanoma
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