Primary pulmonary synovial sarcoma: a clinicopathologic, immunohistochemical, and molecular study of 11 cases.

Primary synovial sarcoma (SS) of the lung is rare and may create diagnostic challenges. We reviewed 11 cases of pulmonary SS (PSS) confirmed by the presence of a tumor-specific SYT-SSX fusion gene to verify their clinicopathologic features including immunohistochemical and genetical profiles. The tumors occurred in 4 men and 7 women (age 29 to 81 years; mean age, 58; median age, 50), and ranged in size from 2 to 15.5 cm (mean, 9 cm). Of the 11 tumors, 10 were a monophasic fibrous type and 1 was a poorly differentiated type. Mitotic rate ranged from 8 to 43 per 10 high-power fields. All cases showed at least focal immunohistochemical positivity for AE1/AE3, CAM5.2 and/or epithelial membrane antigen. High proliferating cell nuclear antigen labeling index (>20%) was found in 8 of 10 cases (80%). Eight (90%) of 9 cases were negative for E-cadherin, and 1 case (10%) exhibited reduced expression of the molecule. The aberrant expression of beta-catenin within cytoplasm and/or nuclei was observed in 6 of 9 (67%) cases. SYT-SSX1 and SYT-SSX2 fusion gene transcripts were detected in 9 and 2 cases, respectively. In 10 patients with follow-up, 3 (30%) had local recurrences, and 4 (40%) developed distant metastases. Five (50%) patients died of the tumor 1 to 9 years after surgery, and 5 (50%) were alive and disease-free in the period ranging from 3 months to 5.5 years. In conclusion, PSS tends to occur in older patients and shows an aggressive behavior probably due to its anatomical location and large tumor often resulting in incomplete resection and high proliferative activity.