We describe a case of a poorly differentiated monophasic
synovial sarcoma arising in the lung of a 50-year-old man. The
tumor, which was located in the right upper lobe, was lobulated, relatively well-circumscribed, and whitish to yellowish in color. Microscopically, it was composed exclusively of ovoid to polygonal or short spindle cells, with a high nuclear to cytoplasmic ratio and relatively scant cytoplasm, arranged in solid sheets or in a hemangiopericytomatous pattern with intervening wiry
collagen fibers. At the periphery of the
tumor, entrapped benign alveolar epithelium produced a pseudo-biphasic appearance. In some areas, an abundance of keloidal
collagen imparted a close resemblance to a
solitary fibrous tumor, making it difficult to establish the diagnosis on the initial needle biopsy, although the malignant nature of the
tumor was suggested because of nuclear
anaplasia. Immunohistochemically, the
tumor was positive for
cytokeratin AE1/AE3,
CAM5.2, EMA,
vimentin, bcl-2
protein,
calretinin, and CD34. The
reverse transcriptase-polymerase chain reaction (RT-PCR), using
RNA extracted from fresh-frozen tissue, demonstrated SYT/SSX-1 fusion transcripts, confirming the diagnosis of
synovial sarcoma. Microscopic examination demonstrated metastatic deposits in hilar lymph nodes. This case indicates that a primary pulmonary
synovial sarcoma, particularly in its poorly differentiated form, is a diagnostically challenging and highly aggressive
neoplasm typically found at an advanced stage.