Acral lentiginous melanoma. A clinicopathologic study of 36 patients.

Acral lentiginous melanoma (ALM) is a distinct variant of malignant melanoma with a predilection for the soles, palms, and nail beds. This melanoma has characteristic histologic features, and its biologic behavior is similar to that of nodular melanoma. It occurs predominantly in the sixth, seventh, and eighth decades of life, with a peak incidence in the seventh decade for males and in the sixth decade for females. Diagnosis of ALM during the radial growth phase is often difficult, and it may not be recognized initially, but treatment in this phase offers an excellent prognosis. There is a high incidence of regressive changes and desmoplasia in ALM; these changes, together with the anatomic peculiarities of nail beds, palms, and soles as compared with other skin areas, make it difficult to determine the Clark's level and to measure the depth of invasion. Wide local excision with lymph node dissection is recommended for subungual melanomas measuring more than 1.00 mm and for lesions showing severe regression. Volar melanomas less than 1.00 mm deep and those in the radial growth phase with minimal invasion require only wide local excision. Amputation of digits and lymph node dissection are recommended for subungual melanomas, if the melanomas exhibit the vertical growth phase. If there is only radial growth without regressive changes, wide local excision is adequate. Patients with metastasis to lymph nodes at the time of diagnosis usually have shorter survival times than do those without lymph node involvement (P = 0.027).