THE ULTRASTRUCTURAL SPECTRUM OF SYNOVIAL SARCOMAS - A STUDY OF THE EPITHELIAL TYPE DIFFERENTIATION OF PRIMARY TUMORS, RECURRENCES, AND METASTASES

Synovial sarcomas (SS) are malignant soft tissue tumors of unknown ori gin. Their classification as carcinomas (monophasic synovial sarcomas, MSS) or carcinosarcomas (biphasic synovial sarcomas, BSS) still raise s controversy. In an attempt to settle this controversy, an ultrastruc tural study was undertaken of 25 primary SS (12 BSS and 13 MSS), 5 rec urrences (3 BSS and 2 MSS), and 2 metastases (2 BSS) based upon precis e selection of different aspects of BSS and MSS on numerous semithin s ections from each case. Ultrastructural markers of epithelial type dif ferentiation of neoplastic cells were found in every type of cellular component of SS regardless of the tumoral pattern (biphasic or not). N o major differences were found between MSS and the nonglandular areas of BSS (not even regarding the presence of abortive glandular lumina). Cytoarchitectural transitions were frequently observed; these include d spindle to epithelioid cell types and fascicular to solid (MSS and B SS) or fascicular to glandular (BSS) patterns. These findings support the assumption that spindle cells of SS are neoplastic and may evolve to glandular cells in SS. Based on the cytogenetic data pointing to a common pathogenesis of both phenotypes (BSS and MSS), SS may represent true carcinomas of soft tissues with a biphasic and/or monophasic pat tern depending on the degree of differentiation.