Malignant mesothelioma versus synovial sarcoma: an analysis of 19 cases with molecular diagnosis

Intrathoracic synovial sarcomas (SSas) are well documented in the literature and characterized by a distinctive t(X;18) translocation. The histologic appearances of a monophasic or biphasic SSa can lead to confusion with biphasic or sarcomatoid mesothelioma (MM). The distinction of pleural SSa from pleural MM is important, because SSas may be responsive to ifosfamide-based chemotherapy and have no proven causal relationship to prior asbestos exposure. Demonstration of the t(X;18) by cytogenetics, fluorescence in situ hybridization (FISH) or reverse-transcriptase polymerase chain reaction is the gold standard for diagnosis, but availability of molecular diagnosis can be limited and testing is time consuming. Recently, it has been suggested that immunohistochemistry (IHC) for transducin-like enhancer of split 1 (TLE) is reliable for diagnosis of SSa and may replace molecular diagnosis.