Keratin in the epithelial-like cells of classical biphasic synovial sarcoma.

Four cases of classical biphasic synovial sarcoma were studied for intermediate filaments of keratin and vimentin type. Epithelial-like cells lining gland-like slits were strongly positive for keratin but negative for vimentin, whereas the spindle cell stroma was negative for keratin but positive for vimentin. The observations indicate epithelial differentiation in the glandular elements of biphasic synovial sarcomas, and are consistent with earlier ultrastructural observations suggesting epithelial properties of these cells.