The wall of the bladder has layers of tissue:
Cancer begins in cells, the building blocks that make up tissues. Tissues make up the bladder and the other organs of the body.
Normal cells grow and divide to form new cells as the body needs them. When normal cells grow old or get damaged, they die, and new cells take their place.
Sometimes, this process goes wrong. New cells form when the body doesn't need them, and old or damaged cells don't die as they should. The buildup of extra cells often forms a mass of tissue called a growth or tumor.
Tumors in the bladder can be benign (not cancer) or malignant (cancer). Benign tumors are not as harmful as malignant tumors:
Bladder cancer cells can spread by breaking away from the original tumor. They can spread through the blood vessels to the liver, lungs, and bones. In addition, bladder cancer cells can spread through lymph vessels to nearby lymph nodes. After spreading, the cancer cells may attach to other tissues and grow to form new tumors that may damage those tissues. See the Staging section for information about bladder cancer that has spread.