Serous cystadenoma of the epididymis of common epithelial ovarian type: case report with an immunohistochemical study.

We report the clinical, morphological and immunohistochemical findings of a case with non-papillary serous cystadenoma of the epididymis. The tumor was a unilocular cyst with a thin fibrous capsule, lined by cuboidal or columnar epithelium containing ciliated cells, mostly arranged in a single layer. Immunohistochemically, the tumor cells were positive for cytokeratin (CK) AE1/AE3 and epithelial membrane antigen (EMA), strongly positive for CK7, progesterone receptor (PR), estrogen receptor (ER), androgen receptor (AR), vimentin, CA-125 and S-100 protein. The cells did not stain for CK20 and CD10. Morphological and immunohistochemical features suggested a mullerian differentiation, possibly originated from vestigial remnants of the Muller duct. This tumor is one of the rare benign lesions which should be considered in the differential diagnosis of a swelling in the epididymal region.