Malignant melanoma in situ arising in the nail unit of a child.

A very rare case of malignant melanoma in situ of the nail unit of a child is presented. Clinically, a pigmented streak was present on the finger nail of a 3-year-old girl, and the lesion increased in size and in darkness of the color associated with periungual pigmentation in the following two years. Histopathologically, sections showed proliferation of atypical melanocytes, arranged mostly in single units but some in nests, in and above the basal layer of the epithelium and admixed with long dendrites and a few mitotic figures. Pigmented lesions of nail units of children often show fading or loss of pigmentation clinically; however, a biopsy should be done when they show augmentative changes which clinically suggest malignancy, because subungual malignant melanoma can exist even in children, and proper biopsy can detect it in its early stages.