Melanoma on palms, soles and beneath nails

Subungual and Acral Lentiginous Melanoma

Acral lentiginous melanoma (ALM) arise on the palms, soles or beneath the nail (subungual melanoma). It is a form of malignant melanoma (MM) characterised by its site of origin. In the past, subungual melanoma (SUM) have always been considered a subtype of ALM. SUM is more common on the feet than hands. Although ALM is a relatively rare type of MM (1-3%), it is the most common subtype of MM in darker skinned people. Bob Marley, black reggae musician, died of an SUM under his toenail.

The proximal nail fold is part of the acral skin which eventually becomes the nail matrix. This is why SUM is naturally considered a subtype of ALM. Melanocytes are present in the nail matrix, but in fewer numbers than in normal skin, and in even fewer numbers in Caucasians. It is thought that these melanocytes do not produce melanin and are inactive.

However, a recent study in the Melanoma Research journal, showed that SUM are perhaps indeed a separate entity to ALM. Compared to patients with ALM, SUM were younger at diagnosis, had higher prevalence of primary MM of the hand, had more frequent reports of previous trauma at the tumour site, and were deeper at diagnosis correlating with an increased frequency of metastases. Interestingly, KIT and KRAS mutations were predominantly found in SUM whereas BRAF and NRAS mutations occurred almost exclusively in ALM.