Primary synovial sarcoma of the kidney

The authors present two cases of primary synovial sarcoma of the kidney. Bo th patients had a mass in the upper part of the right kidney without any pr imary extrarenal neoplastic lesions. Grossly, the tumors were soft to rubbe ry masses measuring 5.5 cm and 5 cm in diameter, respectively. Histological ly, both tumors were poorly differentiated synovial sarcoma. The lesions ex hibited a hypercellular solid or lobular growth of round, oval, or short sp indle cells in variably solid sheets, in intersecting fascicles, or in a ha phazard fashion. Areas of solid aggregation or fascicles of the tumor cells alternating with hypocellular myxoid tissues, together with areas displayi ng a prominent hemangiopericytoma-like pattern, were found. Immunohistochem ically, vimentin was diffusely positive and a few tumor cells were positive fur cytokeratin, epithelial membrane antigen, and neurofilament. The tumor cells were negative for S-100 protein, CD34, smooth muscle actin, and desm in, whereas CD56 and CD99 were positive. In both cases, reverse transcripti on-polymerase chain reaction using ribonucleic acid extracted from formalin -fixed, paraffin-embedded tissues detected SYT-SSX2 fusion gene transcripts , which are characteristic molecular findings of synovial sarcoma. One pati ent died 10 months after diagnosis. These tumors are unique cases of primar y synovial sarcoma of the kidney confirmed by molecular study.