We describe the case of a 53-year-old woman with a history of localized breast cancer who presented with flank pain and was found to have new-onset obstruction of the left ureteropelvic junction. Although initially believed to be unrelated to her history of prior malignancy, intraoperative assessment of tissue from the ureteropelvic junction during planned laparoscopic pyeloplasty revealed urothelial infiltration by carcinoma of breast origin.