Tissue microarray based immunohistochemical study of TLE1 in synovial sarcoma and its histologic mimics

BACKGROUND AND AIMS: Molecular analysis is gold standard for diagnosis of synovial sarcoma (SS) but use of these ancillary techniques is limited by many practical issues like cost and limited resources. Several studies analyzed TLE1 as a diagnostic immunohistochemical marker for synovial sarcoma and few studies disagreed. The objective of the study was to evaluate immunohistochemical expression of TLE1 in synovial sarcoma and its histological mimics. METHODS: The study included a total of 63 cases; of which 28 were synovial sarcomas (SS) and 35 its histologic mimics. A tissue microarray was constructed from these cases and subjected to TLE immunostaining. Nuclear immunoreactivity of TLE1 was graded as 0, 1+, 2+ and 3+ based on intensity and percentage of cells. RESULTS: All SS except one (27/28; 96.4%) were positive for TLE 1. These included 18 of monophasic spindle cell type (94.7%), 5 biphasic type (100%), followed by two each (100%) of poorly differentiated and calcifying type of SS. Of the other tumours 2 GISTs (50%), 2 haemangiopericytoma (66.7%), 2 schwannomas (50%) and one mesenchymal chondrosarcoma (33.3%) were positive for TLE1. CONCLUSION: TLE 1 is a highly sensitive marker with reasonable specificity for synovial sarcoma. Awareness of TLE1 expression in other tumours, is important to avoid misdiagnosis.