Transducer-like enhancer of split 1 (TLE1) as a novel biomarker for diagnosis of synovial sarcoma correlates with translocation t(X;18): a study of 155 cases in China.

Synovial sarcoma (SS) is a mesenchymal tumor of uncertain histogenesis which is defined by the translocation t(X;18). Transducer-like enhancer of split 1 (TLE1) as a new immunomarker for SS has offered an alternative to pathologists in distinguishing synovial sarcoma from other mesenchymal neoplasms, especially in limited molecular facilities. The main aim was to study the expression and diagnostic specificity and sensitivity of TLE1 in SS. We performed this immunohistochemical study on 155 SS (107 monophasic, 35 biphasic, and 10 poorly differentiated), 10 fibrosarcomas, 10 angiosarcomas, 10 epithelioid sarcomas, 10 Ewing sarcoma/PNETs and 8 malignant peripheral nerve sheath tumors (MPNST) using TLE1 immunomarker. Furthermore, in problematic cases (n=43), molecular confirmation was performed by fluorescent in situ hybridization (FISH) to detect the t(X;18) translocation. We correlated the TLE1 overexpression with the t(X;18) and other established biomarkers (CD117, CD56, cytokeratin AE1/AE3, EMA, CD99, BCL2, VIM, CD34, S100, Ki67, SMA). TLE1 expression was observed in 76.19% (112/147) of the SS, including 75.96% (79/104) of monophasic, 78.79% (26/33) of biphasic, and 70% (7/10) of poorly differentiated type. 65.99% (97/147) of SS cases showed a strong to moderate staining of TLE1. Other mesenchymal tumors showed very low or absent staining of TLE1 (