Immunohistochemical examination of mucinous cystadenoma of the testis

A case of mucinous cystadenoma of the testis in a 55-year-old man is reported. The tumor was confined to the testis and was clearly separated from the epididymis. There was no connection between the tumor cyst and the rete testis. The lumen of the cyst was lined with a single-layer of columnar cells interspersed with goblet cells. There was neither stromal invasion nor metastasis to other organs and there were no ovarian or germ cell neoplastic elements in the tumor. Immunohistochemical analysis revealed that MUC2, MUC5AC, carcinoembryonic antigen, CA19-9, CK7 and CK20 proteins were expressed on the tumor epithelial cells, whereas expression of MUC6, alpha-fetoprotein, CA125, human chorionic gonadotrophin, estrogen receptor, progesterone receptor, calretinin, chromogranin A, p53, cyclin D1 and bcl-2 proteins was absent. Ki-67 protein was weakly and sparsely expressed in the nuclei of epithelial cells. The mucinous cystadenoma in the present case, which was devoid of a connection to testicular appendices and had the immunohistochemical characteristics of gastrointestinal mucosa, might have originated from one-sided differentiation of teratoma cells.