Abstract
Sarcomatoid variant of urothelial carcinoma (SV-UC) is an uncommon and highly aggressive tumor with biphasic malignant epithelial and mesenchymal differentiation. Accounting for less than one percent of all urothelial carcinomas, most cases originate in the bladder but may also involve the renal pelvis and ureters. Clinically, SV-UC resembles other urothelial carcinomas with symptoms such as macroscopic hematuria, fatigue, weight loss, and urinary obstruction. SV-UC is often diagnosed at an advanced stage with metastases and a poor prognosis, presenting a diagnostic challenge due to its similarities with other pseudosarcomatous lesions. In this case, we report a 54-year-old male with hypertension who presented with a painless, rapidly enlarging abdominal mass initially suspected to be renal cell carcinoma. Imaging revealed an atrophic right kidney with renal calculi, cortical thinning, and cystic degeneration. The patient underwent nephrectomy, and histopathology confirmed SV-UC of the renal pelvis with mesenchymal differentiation, likely metastatic to the liver and lungs. This case highlights the diagnostic and therapeutic challenges posed by SV-UC of the renal pelvis. More research is necessary to develop standardized treatment protocols for improved outcomes in this rare but aggressive malignancy with a poor prognosis.