Radiation-Induced Synovial Sarcoma of the Lung Diagnosed by Gene Analysis after the Surgical Resection of Chondrosarcoma Arising from the Scapula

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The patient was a 62-year-old male who underwent wide resection and radiotherapy for right scapular chondrosarcoma 12 years ago. An abnormal shadow was detected in the right upper lung field included in the irradiated field on chest X-ray. Since the nodule tended to enlarge, a malignant lung tumor was suspected, and surgery was performed. On histological examination, spindle cells densely proliferated in a bundle pattern. Vimentin, bcl-2 protein, and CD99 were positive, and CD34, cytokeratin, AE1/AE3, and EMA were partially positive on immunohistochemical staining. The SYT-SSX (synaptotagmin- synovial sarcoma X) fusion gene was detected employing RT-PCR, based on which primary synovial sarcoma of the lung was diagnosed. The findings also matched the diagnostic criteria of radiation-induced sarcoma, suggesting radiation-induced primary synovial sarcoma of the lung. Primary synovial sarcoma of the lung is a rare tumor. It is difficult to diagnose based on cellular findings, and immunohistochemical and genetic investigations are essential. Radiation-induced sarcoma may develop through a long-term course, as seen in this patient, for which long-term follow-up after radiotherapy is important.