Subungual melanoma (SUM) is a subtype of acral melanoma. Its incidence in dark phototypes, Hispanics and Asians, is around 20% and accounts for 50% of acral melanomas. It is an infrequent subtype in Caucasians representing only 3%. Subungual melanoma arises from dormant melanocytes in the nail matrix and exceptionally from melanocytes in the nail bed. In its initial phases of radial growth, it presents as longitudinal melanonychia. The differential diagnoses are melanocytic activation (racial, traumatic), nail matrix nevi, and lentigos. Prognosis depends on Breslow depth at diagnosis. For in situ melanoma, treatment consists of conservative surgical removal of the nail unit with 5 mm margins.
Part of the book: Cutaneous Melanoma