Abstract
The prognosis of malignant melanoma has been improving recently in Japan. One of the possible explanations for the favorable prognosis observed in the past 2 decadesis the increase in the number of stage I and II cases of acral lentiginous melanoma. Concurrently with such a trend, melanoma in situ has also increased in incidence. We have experienced 40 cases of melanoma in situ in the past 25 years. A clinicaldiagnosis of melanoma in situ was made in 27 of 40 cases; in the remaining 7 were diagnosed as pigmented nail streaks and 6 as acquired melanocytic nevus. Of the 40 lesions, 250 ccurred on the acral regions, 8 on the face, 6 on the oral mucousmembrane, and the remaining one on the trunk. No cases involved the extremitiesother than hands and feet. There was no sex difference, but female cases were predominant in the lesions developing on the mucous membrane and face. Almost all histological specimens showed the lentiginous type of proliferation of tumor cells. Corresponding to the fact that ALM is the most common type in the Japanese, thepredisposing sites for melanoma in situ in Japan were also the acral regions.
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