Health A-Z

Medical Content Created by the Faculty of the
Harvard Medical School

Bladder Cancer

What Is It?

Bladder cancer is an uncontrolled growth of abnormal cells in the bladder, the balloonlike organ that both stores and expels urine.

The inner lining of the bladder, which comes into contact with the newly formed urine, is called the superficial lining of the bladder. It is lined with transitional cells that are called urothelium. Beneath this lining of cells is a muscular layer that is responsible for the bladder contractions that expel the urine through a tube called the urethra. (As an aside, the bladder receives urine from the kidneys through a tube called the ureter). On the outside of the muscular bladder wall is the outer lining called the serosa, which is in close approximation to fatty tissue or adipose tissue, or lymph nodes.

Bladder cancer begins in the lining of the bladder. In 70% to 80% of people with bladder cancer, the cancer is discovered when it is still a limited, superficial problem, located on the inner lining of the bladder wall. These cancers, which arise on the superficial lining of the bladder (so called superficial cancers), usually appear as an isolated patch of abnormal cells on the bladder lining or as an odd, fingerlike projection (called papillary transitional cell cancer) along the bladder's inner wall. Less often, the tumor is diagnosed when it already has become invasive, which means the tumor has invaded deeply into the muscle of the bladder wall, spread (metastasized) to nearby lymph nodes or spread to distant organs.

There is also a type of bladder cancer called carcinoma in situ. While this cancer has not yet invaded into the deeper muscle portion of the bladder, it can cause symptoms of burning when urinating. Often it isn't visible when the urologist examines the bladder with the aid of a cystoscope. It is diagnosed with a biopsy taken of what appears to be a reddening of the superficial lining. It can also show up in an examination of the shed cells of the urine, in a test called a urine cytology. In this examination, a sample of urine is examined under the microscope for the presence of cancerous cells.

There are three types of bladder cancer, which have different types of cells. About 90% of cancers in the bladder are transitional cell carcinomas. The rest are either squamous cell carcinomas (6% to 8%) or adenocarcinomas (2%).

The causes of bladder cancer are only partly understood. It is thought that the majority of transitional cell carcinomas are caused by carcinogens (cancer-causing substances), such as tobacco smoke and chemicals in the environment. Smokers get bladder cancer two to four times more often than people who don't smoke, although only about half of all bladder-cancer patients have ever been smokers. Bladder cancer also is associated with exposure to certain industrial chemicals, but exposure to such chemicals has been reduced dramatically by modern workplace safety laws. These industrial carcinogens include aniline dyes, polycyclic aromatic hydrocarbons (such as 2-naphthylamine, 4-aminobiphenyl or benzidine), polychlorinated biphenyls or chemicals used in aluminum manufacturing. These chemicals are used in the aluminum, rubber, chemical and leather industries, as well as by dry cleaners, chimney sweeps, hairdressers, painters, printers, textile workers, machinists and truck drivers. In developing countries, a parasitic infection called schistosomiasis increases the risk of developing bladder cancer. Patients who have had long standing bladder stones may have a higher incidence of bladder cancer, in part due to chronic irritation and inflammation of the bladder lining.

Bladder cancer tends to return in people who have had the disease. After bladder cancer is treated, there is a significant likelihood that additional cancers will occur in other locations either within the bladder itself, in the ureters (the tubes that drain the urine from the kidneys into the bladder) or in the part of the kidney called the renal pelvis. The risk of additional cancers developing elsewhere in the urinary tract means that once you have had one episode of bladder cancer, you need to be monitored. This concept is important, because the transitional cells that line the bladder are the same cells that line the ureter, urethra and inner lining of the kidney (the kidney pelvis).

In the United States, bladder cancer is the fourth most common cancer among men and the ninth most common among women. About 63,000 new cases are diagnosed each year, most of them in adults older than 55. Caucasians are two times more likely to develop bladder cancer than are African-Americans, and the illness is three times more likely to affect men than women. Bladder cancer kills approximately 13,000 Americans each year.