Histological type and biological behavior of primary cutaneous malignant melanoma. 2. An analysis of 86 cases located on so-called acral regions as plantar, palmar, and sub-/parungual areas.

Primary cutaneous malignant melanomas are generally divided into 3 separate clinico-pathological variants, lentigo maligna melanoma (LMM), superficial spreading melanoma (SSM), and nodular melanoma (NM). Recently an additional variant, acral lentiginous melanoma (ALM), has been defined, occurring on acral regions, defined as plantar, palmar, and sub-/parungual areas. Histological examination of 86 primary melanomas on acral regions revealed 24 (28%) acral lentiginous melanomas (ALM), 23 (27%) superficial spreading melanomas (SSM), 18 (21%) nodular melanomas (NM), and 21 (24%) unclassifiable melanomas. No LMM was seen. The prognosis was found to be the same in patients with SSM and ALM. However, by correlating histological type with frequency of antecedent nevus, duration of melanoma and dominant invasive tumor cell, it was demonstrated that histologically typical ALM differed from histologically typical SSM by their infrequent origin from antecedent nevi, their lower local growth rate, and their more frequent content of spindle cells. These findings support ALM as a valid melanoma subtype only when clearly defined histologically.