Subungual Melanoma.

Subungual melanoma is a rare form of melanoma that presents a unique set of challenges largely based on the complex anatomy of the nail unit. Subungual melanoma often first appears with longitudinal melanonychia. Thus, practitioners must have a high clinical suspicion in any patient with longitudinal melanonychia and a low threshold for a biopsy. The "ABCDEF" guide can be a useful tool to aid in screening any lesion of the nail bed. The authors recommend that biopsies of the nail unit be performed by a surgeon with an in-depth understanding of the pathoanatomy of subungual melanoma.