The urinary tract consists of the kidneys, the ureters, the bladder, and the urethra. The urinary tract is lined with transitional cell urothelium from the renal pelvis to the proximal urethra. Most cancers that form in these tissues are transitional cell carcinomas. Transitional cell carcinoma of the bladder can be low-grade or high-grade:
Low-grade bladder cancer often recurs in the bladder after treatment but rarely invades the muscular wall of the bladder or spreads to other parts of the body. Patients rarely die from low-grade bladder cancer.
High-grade bladder cancer commonly recurs in the bladder and also has a strong tendency to invade the muscular wall of the bladder and spread to other parts of the body. High-grade bladder cancer is treated more aggressively than low-grade bladder cancer and is much more likely to result in death.
Bladder Cancer Treatment-Health Professional Version, National Cancer Institute (updated Apr. 12, 2018), https://www.cancer.gov/types/bladder/hp/bladder-treatment-pdq