Small-cell epidermoid carcinoma with melanocyte colonization arising in a mature ovarian cystic teratoma.

A case of small-cell epidermoid carcinoma, a rare tumor of the aerodigestive tract, is presented arising in a mature cystic teratoma of the ovary in a 69-year-old woman. Microscopically the small-cell epidermoid carcinoma had a uniform cell population with focal differentiation into keratinous cells. Both the small and keratinized cells were positive for epithelial membrane antigen and CAM 5.2 but negative for vimentin and neuroendocrine markers. This tumor is different from other recently described primary and metastatic small-cell tumors of the ovary. Furthermore, this small-cell epidermoid carcinoma behaved in a nonaggressive fashion. Melanocyte colonization seen in the small-cell epidermoid carcinoma areas of the tumor was a result of its invasion of preexistent areas of a teratoid blue nevus. The staining pattern of HMB-45 demonstrated that pigment was transferred to, but not produced by, the neoplastic small cells.