Cancer that forms in tissues of the bladder (the organ that stores urine). Most bladder cancers are transitional cell carcinomas (cancer that begins in cells that normally make up the inner lining of the bladder). Other types include squamous cell carcinoma (cancer that begins in thin, flat cells) and adenocarcinoma (cancer that begins in cells that make and release mucus and other fluids). The cells that form squamous cell carcinoma and adenocarcinoma develop in the inner lining of the bladder as a result of chronic irritation and inflammation.
Bladder cancers are divided into several types based how their cells look under a microscope. Different types can respond differently to treatments.
Transitional cell (urothelial) carcinoma - This is by far the most common type of bladder cancer. More than 9 out of 10 bladder cancers are this type. The cells from transitional cell carcinomas (TCCs) look like the urothelial cells that line the inside of the bladder.Urothelial cells also line other parts of the urinary tract, such as the lining of the kidneys (called the renal pelvis), the ureters, and the urethra, so TCCs can also occur in these places. In fact, patients with bladder cancer sometimes have other tumors in the lining of the kidneys, ureters, or urethra. If someone has a cancer in one part of their urinary system, the entire urinary tract needs to be checked for tumors.
Bladder cancers are often described based on how far they have invaded into the wall of the bladder:
A bladder cancer can also be described as superficial or non-muscle invasive. These terms include both non-invasive tumors as well as any invasive tumors that have not grown into the main muscle layer of the bladder.
Transitional cell carcinomas are also divided into 2 subtypes, papillary and flat, based on how they grow.
If either a papillary or flat tumor grows into deeper layers of the bladder, it is called an invasive transitional cell (or urothelial) carcinoma.
Other cancers that start in the bladder - Several other types of cancer can start in the bladder, but these are all much less common than transitional cell (urothelial) cancer.
Squamous cell carcinoma: Under a microscope, the cells look much like the flat cells that are found on the surface of the skin. Nearly all squamous cell carcinomas are invasive.
Adenocarcinoma: Only about 1% of bladder cancers are adenocarcinomas. The cancer cells have a lot in common with gland-forming cells of colon cancers. Nearly all adenocarcinomas of the bladder are invasive.
Small cell carcinoma: Less than 1% of bladder cancers are small-cell carcinomas, which start in nerve-like cells called neuroendocrine cells. These cancers often grow quickly and typically need to be treated with chemotherapy like that used for small cell carcinoma of the lung.
Sarcoma: Sarcomas start in the muscle cells of the bladder, but they are rare.
These less common types of bladder cancer (other than sarcoma) are treated similar to transitional cell cancers, especially for early stage tumors, but different drugs may be needed if chemotherapy is required.