Diagnostic value of TLE1 for synovial sarcoma: immunohistochemical analyses of genetically confirmed synovial sarcomas and nonsynovial sarcomas

Synovial sarcoma is a relatively common soft tissue malignancy that is characterized by a specific chromosomal t(X;18)(p11;q11) translocation. Transducin-like enhancer of split 1 (TLE1) has emerged as a useful marker for the diagnosis of synovial sarcoma. However, the diagnostic value of this antibody remains controversial. We investigated TLE1 expression in sixty-two fluorescence in situ hybridization-confirmed synovial sarcomas and three hundred twenty-two nonsynovial sarcomas using TLE1 immunohistochemical staining in tissue microarrays. Furthermore, the expressions of traditional immunohistochemical markers, including epithelial membrane antigen (EMA), AE1/AE3, CK7, Bcl-2 and CD99, were detected in the synovial sarcomas and compared with the expression of TLE1. The results showed that fifty-eight of the 62 (94%) synovial sarcomas were positive for TLE1. Twenty-four displayed 3+ staining (39%), 20 displayed 2+ staining (32%) and 14 displayed 1+ staining (23%). In contrast, 9% (30/322) of the nonsynovial sarcomas stained for TLE1 to various degrees. Notably, only 4% (12/322) of these tumors exhibited 2+ or 3+ staining, and these tumors included malignant peripheral nerve sheath tumors, solitary fibrous tumors, schwannomas and neurofibromas. Regarding the diagnosis of synovial sarcoma, the sensitivity and specificity of TLE1 were 94% and 91%, respectively. EMA staining was positive in 87% of the synovial sarcomas, Bcl2 in 85%, AE1/AE3 in 61%, CK7 in 35% and CD99 in 24%. TLE1 is highly sensitive for synovial sarcomas and more sensitive than traditional immunohistochemical markers. This antibody can be used as a useful screening marker for synovial sarcomas, although complementary molecular studies remain the gold standards for this entity.