Synovial sarcoma of the kidney.

The renal parenchyma is a rare site of origin for primary synovial sarcoma (SS). The present study describes the clinicopathologic, immunohistochemical, and molecular analysis of 7 cases of SS occurring in the kidney. There were 5 female and 2 male patients, with an age range of 15 to 46 years. They presented with solitary renal masses ranging in size from 10.0 cm to 17.0 cm in greatest dimension. Radical nephrectomy was performed in all cases. On gross examination, tumors were large, partially necrotic, and were seen to contain smooth-walled cysts in 4 cases. Histologically, the tumors were characterized by monomorphic spindle cells with indistinct cell borders arranged in intersecting nodular foci with hypocellular myxoid areas, together with a prominent hemangiopericytomatous pattern. The cysts were lined by hobnailed cells with eosinophilic cytoplasm. Immunohistochemically, BCL-2 was positive in all 6 cases in which it was performed, followed by vimentin (4/5 cases), MIC2 (CD99; 2/5 cases), calponin (2/2 cases), and epithelial membrane antigen (1/4 cases). Stains for cytokeratin and CD34 were consistently negative. Reverse transcription-polymerase chain reaction (RT-PCR) using RNA extracted from formalin-fixed paraffin-embedded tissues was carried out in 4 cases and SYT-SSX fusion gene transcript, which is the diagnostic hallmark of SS, was detected. Two patients developed pulmonary metastasis and died 6 and 12 months after diagnosis, respectively. This series of cases is distinct in terms of its morphological spectrum and confirmation by molecular technique.