Malignant melanoma of mucous membranes. A clinicopathologic study of 13 cases in Japanese patients.

We found 13 mucosal melanomas (13%) among 103 cases of malignant melanoma at Tohoku University Hospital, Sendai, Japan, a high incidence. Five melanomas were found on the oral mucosa, another five on the genital mucosa, two within the nasal cavity, and one on the esophagus. Three of the melanomas on the oral mucosa occurred on the lip and the other two on the gingiva. A striking prevalence of melanomas was observed in women, the male-to-female ratio being 0.08. Histologic examination revealed that 58% of the melanomas were characterized by lentiginous, 23% by nodular, and 15% by superficial spreading proliferation. Most of the melanomas were Clark's level IV or V at the time of diagnosis. Except for three who have been under observation for a short time, all the patients have died. There appear to be some clinical and histologic similarities between mucosal melanoma and melanoma of the volar skin, but the difference in biological behavior warrants that the two be classified separately.