Chain-specific keratin profile of epithelioid soft-tissue sarcomas - An immunohistochemical study on synovial sarcoma and epithelioid sarcoma

Although recognized as distinct clinical entities, the putative histogenetic relationship of synovial sarcoma and epithelioid sarcoma remains unclear. We studied the expression of keratin (CK) subtypes of 26 biphasic and 12 monophasic spindle-cell synovial sarcomas, and 12 epithelioid sarcomas with a panel of chain-specific monoclonal CK antibodies and compared them with other epithelioid bone and soft-tissue tumors. The epithelial part of biphasic synovial sarcoma showed abundant immunoreactivity for glandular type CKs 7, 8, 18, and 19, and for basal-cell-type CK14 (81% of cases). Squamous (nonkeratinized) type CK13 was less common (41%), and there was sparse staining for squamous (keratinized) type CK10. Monophasic synovial sarcoma displayed scattered presence of CKs 8/18 in all, and CKs 7, 14, and 19 in a majority of cases. Epithelioid sarcoma exhibited CKs 8/18 in all, and CKs 14 and 19 in about half of the cases, but lacked immunoreactivity for CK7. Chordoma, stained for comparison, displayed massive staining for CKs 7, 8, 18, and 19. Compared with monophasic synovial sarcoma, the epithelial component of biphasic synovial sarcoma shows a diversity of chain-specific CK immunoreactivity, the most variable of all epithelioid neoplasms arising in nonepithelial tissues. The CK profile of epithelioid sarcoma reveals more limitation, which underscores its clinicopathological distinctness, The absence of CK7 in epithelioid sarcoma may be of use in the differential diagnosis with metastatic adenocarcinoma and synovial sarcoma, especially when the epithelial component of the latter is dominating and gland formation is absent.