Unusual pelvic mass in a young adult: prostatic Ewing's sarcoma with distant metastases

Ewing's sarcoma is an aggressive small round cell tumour that usually arises from bone or soft tissues in children and young adults. Primary origin within the prostate is exceptionally rare, with only isolated cases documented. We describe a man in his 20s who presented with urinary obstruction, constipation and leg pain. Imaging revealed a bulky pelvic mass arising from the prostate and bilateral hydroureteronephrosis. Histology demonstrated a round cell neoplasm with strong CD99 and FLI1 positivity, confirming Ewing's sarcoma. Staging PET-CT identified widespread metastases involving lung, liver and bone. The patient underwent urinary and bowel diversion, followed by Vincristine, Adriamycin, Cyclophosphamide alternating with Ifosfamide and Etoposide (VAC/IE) chemotherapy. He achieved complete metabolic remission, allowing colostomy reversal and is currently under surveillance. This case illustrates the need to consider rare sarcomas in the differential diagnosis of pelvic masses in young men with normal serum PSA and highlights the potential for durable response with timely systemic therapy.