Epithelial Differentiation in Synovial Sarcoma Correlation with Histology and Immunophenotypic Expression

The epithelial properties of the cells in six cases of synovial sarcoma, five biphasic and one monophasic, were examined. Epithelial cells formed well demarcated glandular nests with a multi or single layered lining, poorly defined nestlike clusters, or appeared as scattered single plump cells in a spindle cell stroma. Keratinization was seen in multi-layered epithelia, and was suggested in single layered epithelia from the presence of some enlarged eosinophilic cells. Immunohistochemically, epithelia lining glands showed reactivity for both low and high molecular weight (MW) cytokeratins, and the reactions for both were strongest in keratinized cells. Clustered or single plump cells showed low MW cytokeratin reactivity. All epithelial cells were negative for the largest cytokeratin (no. 1), and occasionally stained positively for vimentin. Spindle-shaped stromal cells usually stained positively for vimentin only. Type IV collagen was distributed linearly around well circumscribed epithelia, but not around poorly defined epithelia or plump cells. Epithelial membrane antigen was distributed linearly along glandular spaces and irregularly or granularly in clustered plump cells. The immunophenotypic epithelialization in synovial sarcoma was restricted, but showed considerable correlation with the histological grade of differentiation. Acta Pathol Jpn 39: 381 387, 1989.