Primary renal Ewing sarcoma with extensive metastatic disease at diagnosis: A case report and literature review.

Primary renal Ewing sarcoma (PRES) is an exceedingly rare and aggressive neoplasm. We report a 43-year-old woman with left flank pain and a palpable abdominal mass. Imaging revealed a large renal mass with adrenal, pulmonary, and osseous involvement, staged cT4N1M1. Biopsy showed a small round blue cell neoplasm positive for CD99, NKX2.2, and FLI-1, with EWSR1-FLI1 fusion confirmed by FISH. Palliative systemic chemotherapy achieved partial symptom control, and the patient remains under multidisciplinary follow-up. This case underscores the need for integrated morphological, immunohistochemical, and molecular diagnosis and shows that multimodal treatment can achieve clinical response despite metastatic disease.