How is pleural synovial sarcoma diagnosed?

Updated: Dec 25, 2019
  • Author: Joseph F Tomashefski, Jr, MD; more...
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Histochemical stains may document mucin, which is resistant to hyaluronidase digestion in biphasic synovial sarcoma. Immunostains for cytokeratin are usually less intense and more focal than seen in mesothelioma. Calretinin may be present in both mesothelioma and synovial sarcoma. Compared to mesothelioma, synovial sarcoma often expresses Bcl-2 and BerEP-4, with absence of the mesothelial marker WT-1. [64, 95]

The differential diagnoses of monophasic synovial sarcoma include malignant SFT, sarcomatoid mesothelioma, spindle cell carcinoma of the lung with pleural involvement, and various primary spindle cell sarcomas, such as leiomyosarcoma, fibrosarcoma, and malignant peripheral nerve sheath tumors. [94] SFT more frequently exhibits the “patternless pattern” of short spindle cells interspersed with dense ropy collagen.

SFTs, like synovial sarcoma, are vimentin- and frequently Bcl-2–positive. CD34 is a useful discriminant since it is positive in SFT and negative in synovial sarcoma. Keratin is also helpful, being present in synovial sarcoma but absent in SFT. [65] Consideration of other entities in the differential diagnoses of synovial sarcoma may be accomplished with careful histological assessment and immunohistochemical staining features.

When in doubt regarding the histological and immunohistochemical diagnosis of synovial sarcoma, documentation of the t(X; 18) translocation should confirm the diagnosis.

Metastatic synovial sarcoma from an extrathoracic soft-tissue primary tumor is a more common than primary pleural synovial sarcoma. Histologically, primary pleural synovial sarcoma is similar to metastatic synovial sarcoma. In any case of synovial sarcoma involving the pleura, the possibility of metastatic spread should be considered and excluded clinically. [8, 37]

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