Intermediate filament proteins in human testis and testicular germ-cell tumors.

Normal testicular tissue and 76 testicular germ-cell tumors of various types were immunohistochemically evaluated for the expression of intermediate filament proteins of different types. In normal testes, the rete testis epithelium was positive to cytokeratin, and the Sertoli cells, stromal cells, and Leydig cells were positive for vimentin. Cytokeratin-positive cells were also found lining atrophic seminiferous tubules and were occasionally seen within nonatrophic seminiferous tubules. The classical seminomas showed vimentin positivity, but this was usually observed in a small number of tumor cells. In addition, nearly half the seminomas contained single cytokeratin-positive cells, some of which were multinucleated and appeared to represent syncytiotrophoblastic giant cells. The tumor cells in embryonal carcinomas, endodermal sinus tumors, and choriocarcinomas displayed cytokeratin positivity. In some embryonal carcinomas vimentin-positive tumor cells were also found, probably representing attempts at further differentiation of the tumor cells. In immature teratomas, both the immature and the mature epithelial structures showed cytokeratin positivity. The stromal components, including cartilage, contained vimentin, and the smooth-muscle elements, desmin. Neural tissue positive for neurofilaments and glial tissue positive for glial fibrillary acidic protein, were observed in 5 and 3 of 15 cases, respectively. It is considered that antibodies to intermediate filaments are suitable tools to characterize the differentiation patterns of testicular germ-cell tumors and have the potential to aid in the differential diagnosis especially between seminoma and embryonal carcinoma.