Melanomas of the palm, sole, and nailbed: a clinicopathologic study.
Acral lentiginous melanoma is a newly recognized subtype of malignant melanoma that occurs on volar and subungual skin. Histologic examination of 69 primary volar and subungual melanomas revealed 31 (45%) acral lentiginous, 18 (26%) superficial spreading, and two (3%) nodular melanomas. Eighteen biopsies were inadequate for subclassification. Seventy-one percent (49/69) occurred on plantar skin, 10% (7/69) on the palm, and 19% (13/69) on nailbeds. Plantar melanomas occurred most frequently on weight-bearing areas, particularly the heel (45%). Most were level 4 or 5 at the time of diagnosis. The overall five-year survival of patients with plantar melanomas was 43%. The mitotic rate showed an inverse relationship with survival. The ratio of volar skin melanomas to subungual melanomas was 4:1. Ninety-two percent of subungual melanoma occurred on the thumb or great toe. The five-year survival for palmar and subungual melanomas was 19%. Our data confirm that acral lentiginous melanoma is a distinct subtype of melanoma with a unique histologic appearance and behavior, but not all volar and subungual melanomas are the acral lentiginous type.