Solitary basaloid follicular hamartoma.

We present a case of solitary basaloid follicular hamartoma of 8 years' duration on the nose of a 55-year-old Japanese man. Clinical examination revealed a solitary, asymptomatic, smooth-surfaced, black papule. Histologically, the lesion showed multifocal proliferation of basaloid cells forming islands, branching cords and anastomosing strands that were continuous with the basal layer of the epidermis. Individual hair follicles were replaced by these undifferentiated basaloid proliferating cells. Some abortive hair follicle-like structures composed of follicular bulbs and contiguous rudimentary dermal papillae were observed. This solitary papular type of basaloid follicular hamartoma is quite rare; our case is clearly distinguished from other neoplasms with hair follicle differentiation as well as from infundibulocystic basal cell carcinoma, which have been the most problematic differential diagnoses in the recent dermatopathologic literature.