Most bladder cancers — about 90 percent — begin in the cells on the surface of the bladder’s inner lining, known as transitional epithelial cells. This type of cancer is called transitional cell carcinoma (TCC) or urothelial carcinoma. Most TCCs are noninvasive, meaning the cancer stays within the bladder’s inner lining.
In about 30 percent of cases, however, TCC tumors eventually penetrate the bladder’s lining and grow into the muscle wall. Muscle-invasive bladder cancer can also metastasize (spread) to other parts of the urinary system, such as the kidneys, ureters, and urethra.
Less common types of bladder cancer can develop in the inner lining of the bladder as a result of chronic irritation and inflammation. These rare types usually grow into the muscle of the bladder over time and are characterized according to the cell type involved.
Squamous cell carcinoma: Approximately 8 percent of bladder cancers begin in the thin, flat squamous cells that may form in the bladder after a long-term infection or irritation.
Small cell carcinoma: Approximately 1 percent of bladder cancers start in the small, nerve-like cells in the bladder called neuroendocrine cells.
Adenocarcinoma: Approximately 1 percent of bladder cancers begin in cells that make and release mucus and other fluids in the bladder.