BIPHASIC SYNOVIAL SARCOMAS ARISING IN THE PLEURAL CAVITY - A CLINICOPATHOLOGICAL STUDY OF 5 CASES

Five cases of primary synovial sarcoma of the pleura are presented wit h a discussion of differentiation from other biphasic malignant neopla sms, most notably malignant mesothelioma. The cases have clinical, his tologic, and immunohistochemical features consistent with synovial sar coma of soft tissue. The average age at initial presentation of the re ported patients was 25 years with an approximate range of 9 to 50 year s. A large pleural-based intrathoracic mass was identified in each cas e. Histologic analysis showed a biphasic (mixed) pattern composed of e pithelial and spindle cells. The epithelial cells showed cleft-like to tubulopapillary growth with focal intraluminal periodic acid Schiff's (PAS)-positive, diastase-resistant secretions identified in four of t he five cases. The spindle cell component was composed predominantly o f densely packed, elongated, fusiform cells. Immunohistochemical stain ing showed positivity with antibodies against cytokeratin, BER.EP4, ep ithelial membrane antigen, and vimentin in all cases. The patients see m to have an aggressive course, with four deaths reported within 3 yea rs from initial surgery. These cases represent the first reported case s of primary synovial sarcoma of the pleura and lend further credence to the theory that synovial sarcomas are derived from immature mesench ymal elements, not from synovium.