Perianal basal cell carcinoma - unusual localization of a frequent tumor.

Basal cell carcinoma is the most common human neoplasia. In more than 80% of patients, who are predominantly elderly, it is located in the head-and-neck-area. Basal cell carcinomas in non-UV-exposed areas of the body, such as the anogenital region, are dermatological rarities. We describe an 88-year-old patient with a perianal tumor that was detected during skin cancer screening. Histopathology showed the tumor to be a basal cell carcinoma. Immunohistochemical staining for Ber-EP4 was highly positive, clearly distinguishing the tumor from basaloid anal carcinoma, which is the most important histological differential diagnosis. Additional virological analyses for human papil-lomaviruses (HPV) were negative. Immunohistochemical staining for p16(INK4a) demonstrated strong expression in the cells of the tumor parenchyma. However, p16(INK4a) can also be expressed independently of HPV. The present case shows that all uncertain perianal skin lesions should be biopsied.