Supplementary Material for: Management of a Patient with Ewing’s Sarcoma of the Kidney: A Case Report

Abstract Introduction: Primary Ewing sarcoma of the kidney (ESK) is an exceptionally rare and highly aggressive malignancy. Its clinical, radiologic, and pathologic features often overlap with other renal tumors, making early diagnosis particularly challenging. Case Presentation: A young adult presented with acute abdominal pain. Contrast-enhanced CT revealed a cystic–solid right renal mass with active intratumoral bleeding. The patient underwent emergency surgical management, followed by a second radical procedure due to uncertain resection margins. Histopathological examination demonstrated sheets of small round blue cells, and immunohistochemistry showed diffuse CD99 and NKX2.2 positivity. Fluorescence in situ hybridization confirmed an EWSR1 gene rearrangement, establishing the diagnosis of Ewing sarcoma. Postoperatively, the patient received a VAC 4-cycle sequential IE 2-cycle adjuvant chemotherapy regimen. Conclusion: This case highlights the diagnostic difficulty and rapid progression of renal Ewing sarcoma. Accurate diagnosis relies on integrated imaging, histopathology, immunoprofiling, and molecular testing. Early recognition and multidisciplinary decision-making are essential for optimizing outcomes in this rare tumor entity.