Acral Melanoma (Palmar-Plantar Melanoma, Volar-Subungual Melanoma)

Abstract

Acral melanoma (AM) may be strictly defined as any melanoma arising on glabrous or volar (non-hair-bearing) skin of the soles, palms, and digits and also from the nail apparatus (22,32,34,81–102). Although the latter anatomic domains are indeed unique, the latter definition is difficult to adhere to since glabrous and nonglabrous skin merge imperceptibly; therefore, some proportion of acral melanomas will involve both glabrous and nonglabrous skin; in addition, some authors have included melanomas of the dorsal skin of the hands and feet as AM. Nonetheless, as discussed here, acral melanomas are strictly defined as involving only glabrous skin or the nail apparatus of the distal extremities. 85% of AM involve volar (palms, soles, and digits) surfaces versus 15% arising from the nail apparatus (subungual areas). Among AM, almost 90% occur on the foot with the following distibution: soles, 68–71%; toes, 11%; subungual areas of the feet, 9–10%; palms, 4%–10%; fingers, 2%; and subungual areas of the hands, 5.6–10% (86). In addition to these topographic considerations, patients with AM are generally older (e.g., commonly 60–70 years of age), have particular histopathologic findings, and may have a different biologic basis compared to other melanomas. There seem to be no clear differences in frequency between men and women. Although rare among white populations (range 1–13.5%), AM is the most frequent form of melanoma among Asians (29–46%), Africans (60–70%), and other ethnic groups of color (22,32) (Table 14). However, it should be emphasized that AM has approximately the same incidence in all ethnic groups (92). Reed and co-workers (83,84) first recognized that melanomas involving glabrous skin of the soles may feature a rather characteristic pattern of lentiginous intraepidermal melanocytic proliferation. However, pagetoid and nested intraepidermal patterns of melanocytes are also frequently present (94,101).