Synovial sarcoma presenting as a lung mass and diagnosed by cytology

Synovial sarcoma is a common soft tissue sarcoma with variable fibrous and epithelial differentiation that rarely arises from other body sites, such as within the lung. A case of a 68-year-old male with an extensive smoking history who presented with chest pain and a primary, central, metabolically active lung mass was reported. The mass was biopsied by bronchial brushing, bronchoalveolar lavage (BAL), and transbronchial fine-needle aspiration (FNA). Cytologic analysis of bronchial brushing, BAL, and FNA revealed single and clusters of atypical spindle cells, oval, or spindle-shaped nuclei with smooth nuclear membranes, hyperchromatic and granular chromatin, scant to moderate and delicate cytoplasm, a high degree of mitotic figures, and a lack of necrosis. Immunohistochemical studies showed that the tumor cells were positive for CD99, BCL2, and CK7. A diagnosis of synovial sarcoma was rendered. The differential diagnosis of primary pulmonary synovial sarcoma is discussed, including neuroendocrine tumors, squamous cell carcinoma, and various sarcomatous tumors.