Pulmonary carcinoid tumor masquerading as a synovial sarcoma.

A rare case of pulmonary carcinoid tumor exhibiting morphologically as a monophasic synovial sarcoma is reported. The patient is a 37-year-old man who presented with shortness of breath for several weeks. The chest computed tomographic scan showed a 3.5 cm pulmonary mass in the left lower lobe.The lesion was an oval, tan nodule displaying features of monophasic synovial sarcoma. Immunohistochemical studies were performed and included a carcinoid tumor as a main differential diagnosis. Reverse transcriptase polymerase chain reaction and fluorescence in situ hybridization studies were negative for a molecular evidence of synovial sarcoma. This case further emphasizes the capacity of pulmonary carcinoid tumor cells to show various morphologic expressions even toward a mesenchymal differentiation mimicking a synovial sarcoma.