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Introduction: Ewings-like sarcoma is a rare subgroup of small round cell sarcoma with immunohistochemistry and morphological similarities to Ewing Sarcoma. We report a rare case of renal pelvis invasive urothelial carcinoma with small round cell sarcoma differentiation showing EWSR1 gene rearrangement. Case: An 84-year-old male presented with 6 months of intermittent painless gross hematuria. Workup revealed a 5.4cm left renal pelvicalyceal mass suspicious for transitional cell carcinoma and a 2.5cm enhancing left renal cortical lesion. The patient underwent an uncomplicated robotic left nephroureterectomy. Pathology revealed small round cell sarcoma composing greater than 80% of the renal pelvis tumor with the remainder composed of conventional invasive high grade urothelial carcinoma. Additionally, there were focal areas resembling chondroid differentiation. FISH examination of the round cell component was positive for a variant complex EWSR1 gene rearrangement. The renal mass was consistent with renal clear cell carcinoma. Margins were negative. Conclusion: This case may be the first documented case of upper tract urothelial carcinoma with small round cell sarcomatoid differentiation showing EWSR1 gene rearrangement. Literature review reveals only one case report of a urothelial carcinoma of the bladder with underlying “Ewing Sarcoma” features. Genetic testing will guide adjuvant chemotherapy recommendations


The 95th Annual Meeting of the North Central Section of the AUA, Chicago, IL, October 6-9, 2021.