Biphasic chest wall synovial sarcoma with epithelial pleural effusion: a diagnostic challenge

Synovial sarcoma (SS) is a rare malignancy that most commonly involves the extremities and large joints. We describe a 67-year-old woman who presented with shortness of breath and flu-like symptoms, and a chest wall mass. On resection of the mass biphasic morphology of SS was noted, as well as confirmatory immunostains including TLE1 and bcl2. An SS18/SSX2 fusion transcript was detected by reverse transcriptase-DNA amplification. A year later, following chemotherapy, the patient developed a right-sided pleural effusion. Cytological examination of the fluid showed an epithelial population forming clusters and groups. TLE1 was positive, as well as fluorescent in situ hybridization analysis for the SS18/SSX2 fusion transcript. SS can be a challenging diagnosis in fluid-filled cavities, when the epithelial component predominates and its original biphasic quality is not seen. We discuss the diagnostic challenges of monophasic and biphasic SS, and updates to ancillary testing.