Large Retroperitoneal Tumor Operated for Suspected Renal Cell Carcinoma Turned Out to be Primary Renal Synovial Sarcoma: A Rare Entity.

Approximately 5%-10% of soft-tissue tumor comprised synovial sarcoma (SS) and are commonly found in close proximity of large joints affecting young adults. However, SS of the kidney is extremely unusual (1%) and has a poor prognosis. There are three subtypes of primary renal SS (PRSS). The monophasic variant is the most common and shares the same clinical, molecular, and ultrastructural features with other subtypes. Histomorphology with immunohistochemistry (IHC) differentiates it from other sarcomas of kidney and sarcomatoid renal cell carcinoma. Genetic analysis reveals specific SYT-SSX2 (X, 18) translocation. Herein, a case of PRSS (monophasic variant) is presented in a 31-year-old female with right-sided loin pain and huge mass of size (11.9 cm × 9.3 cm × 10 cm) without associated hematuria. It was clinically thought to be renal cell carcinoma. Radical nephrectomy was performed, followed by histopathology and IHC which suggested PRSS. Then, combined chemotherapy of doxorubicin with cyclophosphamide was rendered, and on follow-up, she is doing well with an uneventful course.