Acral lentiginous melanoma (ALM) is a subtype of melanoma that occurs on acral surfaces. It presents as an atypical pigmented lesion on the distal extremities, including the palms, soles, and subungual areas. As in other locations, ALM may be amelanotic in these areas, in which case, a reddish, pinkish, or skin-colored macule, plaque, or nodule is seen. Ulceration may occur and be the predominant finding in long-standing or rapidly growing tumors. The most common location for ALM is on a lower extremity (about 78.3%), and it occurs frequently on the hallux and thumb. The incidence of ALM in men and women is similar, and it most commonly occurs in those aged 50-60 years. ALM accounts for less than 5% of all melanomas.

ALM occurs in all races and ethnicities with a similar incidence; however, it is disproportionately represented compared with other melanoma subtypes among individuals with darker skin colors, including those of African, Hispanic, and Asian descent. In these individuals, the diagnosis is often delayed, and therefore the prognosis is worse than in individuals with lighter skin colors.

Because ALM typically occurs in minimally sun-exposed areas in patients of all phototypes, it has been suggested that sun exposure is less of a risk factor than in the other subtypes of melanoma, indicating other possible etiologies. This has led to the theory that trauma may be a risk factor leading to the development of ALM, and some studies have shown an association with injuries to the foot. Also, ALM occurs more frequently at physically stressed and weight-bearing sites of the volar region and nail apparatus. A pattern of spread has been observed with the long axis along natural creases on the sole. Genomic studies have also revealed different mutational profiles compared with other melanoma subtypes and identified KIT mutations in a subset of acral melanomas.