Abstract
Ewing sarcoma family tumors (ESFTs) of the kidney represents less than 1% of all renal tumors. A 45-year-old Japanese woman presented with right abdominal pain. Contrast-enhanced computed tomography showed a 12 × 8-cm right cystic renal mass. The mass was diagnosed as cystic renal cell carcinoma (RCC) and right partial nephrectomy was performed. Immunohistochemical studies showed that the tumor was positive for CD99 (membranous staining in tumoral cells), indicating ESFT. The patient is doing well without further therapy after 1 year of follow-up. To our knowledge, this is the first report of renal ESFT mimicking cystic RCC on diagnostic imaging.