Atypical fibrous histiocytoma of the scrotum.

Atypical fibrous histiocytoma is a rare neoplasm. A scrotal location for this tumor is even more unusual. We report a case of a 90-year-old man with scrotal atypical fibrous histiocytoma. Our case had histologic features consistent with those cases previously reported in the literature. The tumor consists of cells with large hyperchromatic irregular nuclei, bizarre multinucleated cells (monster cells), and xanthomatous cells with large prominent nuclei set in a background of classic fibrous histiocytoma. Rare mitotic figures are identified. Immunohistochemical studies showed the tumor cells to be positive for vimentin, smooth muscle actin, desmin, KP-1, factor XIIIa, and MIB-1 (less than 10%). In addition to the expected immunohistochemical studies, the tumor stained diffusely positive for CD117. To our knowledge, this is the first report of atypical fibrous histiocytoma of the scrotum.