Introduction: Primary synovial sarcoma of the lung is an extremely rare tumor, accounting for less than 0.5% of all lung tumors. The diagnosis is established only after sarcoma-like primary lung malignancies and metastatic sarcoma have been excluded.

Case Report: A 70-year-old female patient was admitted to our hospital because of a right lower lobe lung mass. Computed tomography-guided needle biopsy revealed the presence of spindle cell sarcoma. The patient underwent right lower lobectomy and combined resection of the pericardium. Histologically, the tumor displayed tubular proliferation of epithelial cells and fascicular proliferation of spindle cells. Immunohistochemically, both tumor cell types were positive for vimentin and bcl-2. Pleomorphic carcinoma or synovial sarcoma was suggested as a diagnosis. We found the presence of SYT-SSX fusion gene transcripts in RNA samples from frozen tissue from the tumor. The final diagnosis was primary pulmonary biphasic synovial sarcoma.

Conclusion: We report an extremely rare case of primary pulmonary biphasic synovial sarcoma. Our findings indicate that molecular detection of SYT-SSX fusion gene transcripts is very helpful and may be necessary when synovial sarcoma is recognized at uncommon sites.

Keywords: Primary pulmonary synovial sarcoma, Synovial sarcoma, SYT-SSX fusion gene transcripts