EWSR1::SSX1 Fusion-Driven Synovial Sarcoma: A Case Presentation and Review of the Literature.

According to the 5th edition of the WHO Classification of Soft Tissue and Bone Tumors, the diagnosis of synovial sarcoma relies on morphology, immunohistochemistry, and the detection of a specific fusion involving the SS18 gene with a member of the SSX gene family. However, few cases of synovial sarcoma that do not harbor such molecular alterations have been recently reported. We present the case of a patient with a diffuse pleural mass and pleural effusion that showed in a core needle biopsy a spindle cell neoplasia morphologically suggestive of synovial sarcoma. An SS18 break-apart FISH was performed with a negative result. Afterwards, an EWSR1::SSX1 fusion was detected by next-generation sequencing. There is scarce literature on non-SS18 fusion-driven synovial sarcomas, and no study has evaluated whether these novel molecular alterations have a relevant clinical impact on patients beyond the diagnostic value.