Pleural malignant mesothelioma versus pleuropulmonary synovial sarcoma: a clinicopathological study of 22 cases with molecular analysis and survival data

The aim of this study was to carry out a comparative analysis by transducin-like enhancer of split 1 (TLE1) immunohistochemistry and molecular analysis of SYT-SSX, for 16 pleural predominantly sarcomatoid mesotheliomas and six cases of pleuropulmonary synovial sarcoma (five pleural in distribution only, with one case of a predominantly subpleural upper lobe synovial sarcoma), all of which were solely or predominantly monophasic. Our comparison included survival and some clinical data. We consider that the following points emerged from this study: • Clear discrimination between pleural sarcomatoid mesothelioma and synovial sarcoma can be impossible from H&E-stained sections and conventional immunohistochemical markers for mesothelioma, and on TLE1 immunolabelling.• In line with current approaches to diagnosis, we defined the mesotheliomas according to their negative SYT-SSX status, versus a positive result by fluorescence in situ hybridisation (FISH) or by reverse transcriptase PCR (RT-PCR) for synovial sarcoma.• In this series, predominantly sarcomatoid mesotheliomas out-numbered the synovial sarcomas in a ratio of ∼3:1.• The synovial sarcomas were diagnosed in patients significantly younger on average than the sarcomatoid mesotheliomas.• The synovial sarcoma patients had significantly longer survivals than the predominantly sarcomatoid mesotheliomas.