Bladder cancer begins when cells in the urinary bladder start to grow uncontrollably. As more cancer cells develop, they can form a tumor and spread to other areas of the body. (To learn more about how cancers start and spread, see What Is Cancer?)
The bladder is a hollow organ in the pelvis with flexible, muscular walls. Its main function is to store urine before it leaves the body. Urine is made by the kidneys and is then carried to the bladder through tubes called ureters. When you urinate, the muscles in the bladder contract, and urine is forced out of the bladder through a tube called the urethra.
Start and spread of bladder cancer
The wall of the bladder has several layers, which are made up of different types of cells (see How is bladder cancer staged? for descriptions of the different layers).
Most bladder cancers start in the innermost lining of the bladder, which is called the urothelium or transitional epithelium. As the cancer grows into or through the other layers in the bladder wall, it becomes more advanced and can be harder to treat.
Over time, the cancer might grow outside the bladder and into nearby structures. It might spread to nearby lymph nodes, or to other parts of the body. (If bladder cancer spreads, it often goes first to distant lymph nodes, the bones, the lungs, or the liver.)
Types of bladder cancer
Several types of cancer can start in the bladder.
Urothelial carcinoma (transitional cell carcinoma)
Urothelial carcinoma, also known as transitional cell carcinoma (TCC), is by far the most common type of bladder cancer. In fact, if you are told you have bladder cancer it is almost certain to be a urothelial carcinoma. These cancers start in the urothelial cells that line the inside of the bladder.
Urothelial cells also line other parts of the urinary tract, such as the part of the kidney that connects to the ureter (called the renal pelvis), the ureters, and the urethra. Patients with bladder cancer sometimes have other tumors in these places, so the entire urinary tract needs to be checked for tumors.
Invasive versus non-invasive bladder cancer
Bladder cancers are often described based on how far they have invaded into the wall of the bladder:
- Non-invasive cancers are still in the inner layer of cells (the transitional epithelium) but have not grown into the deeper layers.
- Invasive cancers have grown into deeper layers of the bladder wall. These cancers are more likely to spread and are harder to treat.
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.
Papillary versus flat cancer
Bladder cancers are also divided into 2 subtypes, papillary and flat, based on how they grow (see image above).
- Papillary carcinomas grow in slender, finger-like projections from the inner surface of the bladder toward the hollow center. Papillary tumors often grow toward the center of the bladder without growing into the deeper bladder layers. These tumors are called non-invasive papillary cancers. Very low-grade (slow growing), non-invasive papillary cancer is sometimes called papillary urothelial neoplasm of low-malignant potential (PUNLMP) and tends to have a very good outcome.
- Flat carcinomas do not grow toward the hollow part of the bladder at all. If a flat tumor is only in the inner layer of bladder cells, it is known as a non-invasive flat carcinoma or a flat carcinoma in situ (CIS).
If either a papillary or flat tumor grows into deeper layers of the bladder, it is called an invasive urothelial (or transitional cell) 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 urothelial (transitional cell) cancer.
Squamous cell carcinoma: In the United States, only about 1% to 2% of bladder cancers are squamous cell carcinomas. 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.
These less common types of bladder cancer (other than sarcoma) are treated similar to TCCs, especially for early stage tumors, but if chemotherapy is needed, different drugs might be used.
Last Revised: 05/23/2016