Ureteral cancer is a rare type of cancer that occurs in the ureters, the tubes that carry urine from the kidneys to the bladder. It usually begins in the cells lining the inside of the ureter and most commonly takes the form of urothelial carcinoma, which also affects the bladder and kidneys. Ureteral cancer can block the flow of urine, leading to kidney problems and, if left untreated, may spread to other parts of the body.