Bladder cancer is a malignant tumour that starts in the superficial cells of the bladder.
Bladder cancer is most commonly found in urothelial cells, also called transitional epithelium. The urothelium lining the inside of the bladder, ureters, urethra and kidney pelvis. It is formed of urothelial or transitional cells. The cancer that starts in urothelial cells is called urothelial or transitional carcinoma. Urothelial carcinomas account for more than 90% of all bladder cancers.
When cancer only affects the urothelium, it is called superficial bladder cancer. If cancer spreads to the connective tissue or muscle of the bladder wall, it is more like an invasive cancer of the bladder.
Rare types of bladder cancer may also occur. Squamous cell carcinoma and adenocarcinoma are examples. Urothelial carcinoma may also originate in the pelvis or ureters, but this is less common.