Metastasis of uterine endometrioid carcinoma mimicking upper tract urothelial carcinoma

Accurate diagnosis of upper-tract urothelial carcinoma is difficult when urine cytology and ureteroscopy are inconclusive. A 59-year-old woman had undergone total hysterectomy for uterine endometrioid carcinoma 5 years earlier. Follow-up computed tomography demonstrated left hydronephrosis and an enhancing mass in the ureter. Urine cytology was negative, but ureteroscopic biopsies revealed malignant cells that were potentially urothelial carcinoma. The patient received left nephroureterectomy, but histopathology unexpectedly showed metastatic uterine endometrioid carcinoma. This case highlights that metastatic relapse of uterine carcinoma can mimic ureteral cancer on imaging. When cytology and biopsy are inconclusive, prior malignancies should remain in the differential diagnosis.