Roles of immunohistochemistry and detection of SYT-SSX fusion gene in diagnosis of synovial sarcoma

Abstract

To assess the diagnostic values of immunohistochemistry and SYT-SSX fusion gene detection for synovial sarcoma. Based on clinical features, histological and immunohistochemical profiles, 195 cases of tumors were divided into three diagnostic categories: definitive synovial sarcoma, probable synovial sarcoma and possible synovial sarcoma. RT-PCR Detection of the SYT-SSX fusion gene was performed using paraffin embedded tissue samples. Comparison between RT-PCR and immunohistochemistry results was carried out and their diagnostic value was evaluated. There were 62 (31.8%) definite synovial sarcomas, 49 (25.1%) probable synovial sarcomas and 84 cases (43.1%) possible synovial sarcomas. SYT-SSX fusion gene was detected in 140 (78.2%) cases overall, including 94.7% (54/57) definite synovial sarcomas, 86.0% (37/43) probable synovial sarcomas and 62.0% (49/79) possible synovial sarcomas. In tumors in the certain and probable synovial sarcoma categories, the positive rates of epithelial membrane antigen (EMA) were significantly higher in the SYT-SSX positive cases than SYT-SSX-negative cases (P = 0.022, P = 0.010, respectively). EMA was positively correlated with the presence of SYT-SSX (r(s) = 0.431, P = 0.001, r(s) = 0.463, P = 0.002, respectively). However, such a correlation was not seen in cytokeratin (CK), vimentin or S-100 protein immunostains (P > 0.05). In tumors of possible synovial sarcoma category, there were no significant differences of CK, EMA, vimentin or S-100 protein between SYT-SSX-positive and SYT-SSX-negative tumors. SYT-SSX fusion gene detection is not needed when the conventional approaches are diagnostic. EMA positivity has a similar diagnostic value to that of SYT-SSX by RT-PCR for tumors in the probable synovial sarcoma category. However, detection of SYT-SSX is very important for diagnosis of the tumors in the category of possible synovial sarcoma.