Acral lentiginous melanoma, light micrograph. Acral lentiginous melanoma (ALM) is the most common type of melanoma in dark-skinned and Asian populations. The most common locations are the thumb, big toe, and the heel. This light photomicrograph shows ALM arising in the heel of an elderly female. The epidermis is markedly thickened. The tumour cells have spindle cell morphology. The tumour infiltrated into the subcutaneous fat (Clark Level 5). Surface ulceration was also present.