Subungual squamous cell carcinoma in Darier's disease.

We report the first case of subungual squamous cell carcinoma in a patient with Darier's disease (keratosis follicularis). The presence of human papillomavirus DNA was confirmed, consistent with its probable role in carcinogenesis at this site. The role of an altered immune state is discussed as an additional factor. Squamous cell carcinomas may be overlooked when they occur among the other cutaneous manifestations and complications of Darier's disease. A solitary, ulcerating nail bed lesion warrants biopsy to exclude squamous cell carcinoma.