Superficial melanomas of oral mucous membranes.

In accordance with microscopic and clinical criteria established for superficial melanomas of the skin (superficial spreading melanoma, lentigo maligna melanoma, acral-lentiginous melanoma), three oral lesions have been evaluated. The literature on oral melanomas has also been reviewed, with special attention given to those cases that had pre-existing melanosis. One patient with a diagnosis of superficial spreading melanoma eventually died of his untreated lesion 11 years after its first appearance. Two patients had lesions diagnosed as acral-lentiginous melanoma (a group which also includes volar and subungual melanomas) that exhibited aggressive, recurrent behavior. These lesions had microsocpic features similar to lentigo maligna melanoma but did not behave in a manner consistent with that diagnosis. Electron microscopic study of one acral-lentiginous melanoma demonstrated malenosomes and premelanosomes that were like those seen in normal melanocytes and nevus cells. The superficial or radial growth phase of many oral melanomas has apparently gone unrecognized. Melanosis has been reported to be a common feature of invasive oral melanomas but has not generally been related to the natural history of these lesions. Oral lesions with a prolonged intra-epithelial or radial growth phase would be expected to have a better prognosis than nodular melanomas, but meaningful survival data are not available because of the infrequency with which oral melanomas have been subclassified.