Synovial sarcoma. An immunohistochemical study of the epithelial component.

Twenty-five synovial sarcomas were studied with a battery of antibodies directed against keratin and epithelial membrane antigen (EMA). The keratin antibody MNF 116 showed reactivity in 24 tumors. In addition, 22 tumors showed reactivity with the antibody Keratin Wide Spectrum, 20 with the antibody Keratin 56, 64, and 19 with CAM 5.2. Seventeen tumors showed reactivity with EMA. The keratin and EMA reactivity was present in cells lining obvious cleft-like structures in biphasic tumors. In the spindle cell areas of both biphasic and monophasic fibrous tumors, we found clusters of a few reacting cells apparently located around small clefts. In the synovioblastic tumors, clusters of plump tumor cells reactive for both the keratins and EMA were present. In conclusion, we found that proper identification of epithelial differentiation in synovial sarcomas is facilitated by an immunohistochemical application of anti-epithelial antibodies. In most tumors, there was immunoreactivity for the same type of keratins as are normally identified in simple epithelia (the antibody CAM 5.2), but also for those found in stratified squamous epithelia (the antibody Keratin 56, 64). The results indicate that screening for epithelial features on paraffin sections in the various types of synovial sarcoma, even the poorly differentiated synovioblastic tumors, is improved if epithelial antibodies with a broad spectrum of reactivity are chosen.