Endodermal sinus tumor: immunophenotypic expression of a carcinoma.

A series of five endodermal sinus tumors was studied for their cytoskeletal and other phenotypic markers. They included 2 ovarian, 2 testicular, and 1 inguinal tumors. The cytoskeletal expression was also studied by gel electrophoresis and immunoblotting. Every tumor was diffusely and strongly immunostained for cytokeratin. By SDS-PAGE and immunoblotting, cytokeratins 8 & 18 were detected. Vimentin was focally coexpressed in 4 cases. The stroma was diffusely immunostained for vimentin. None of them expressed desmin, neurofilament, or glial filament protein. Desmoplakin was expressed only in one ovarian tumor. Alpha-fetoprotein and S-100 protein were also diffusely positive among the neoplastic cells; intracytoplasmic globules were especially strongly immunostained. These findings suggest that endodermal sinus tumors represent a group of pure malignant epithelial neoplasms, and may be regarded as primitive carcinomas.