The following is provided by the National Cancer Institute
Bladder cancer is diagnosed in 38,000 men and 15,000 women each year, primarily affecting men and women over the age of 40, each year in the U.S. This is the fourth most common type of cancer in men, and the eighth most common in women. Studies have found the following risk factors for bladder cancer:

Use of tobacco is a major risk factor. Cigarette smokers are two to three times more likely than nonsmokers to get bladder cancer. Pipe and cigar smokers are also at increased risk.

Carcinogens in the workplace. Workers in the rubber, chemical, and leather industries are at risk, as are hairdressers, machinists, metal workers, printers, painters, textile workers, and truck drivers.

Being infected with certain parasites. These parasites are common in tropical areas but not in the United States.

Caucasians get bladder cancer twice as often as African Americans and Hispanics. The lowest rates are among Asians. People with family members who have bladder cancer are more likely to get the disease. Researchers are studying changes in certain genes that may increase the risk of bladder cancer. Also, people who have had bladder cancer have an increased chance of getting the disease again.

Researchers have been studying chlorine by-products found in water for more than 25 years. So far, there is no proof that chlorinated water causes bladder cancer in people. Studies continue to look at this question. Some studies have found that saccharin, an artificial sweetener, causes bladder cancer in animals. However, research does not show that saccharin causes cancer in people.

The wall of the bladder is lined with cells called transitional cells (these are cells that vary in shape depending on whether the tissue is being stretched – they may be stretched without breaking apart) and squamous cells, which are flat cells that look like fish scales under a microscope. More than 90 percent of bladder cancers begin in the transitional cells. This type of bladder cancer is called transitional cell carcinoma. About 8 percent of bladder cancer patients have squamous cell carcinomas.

Cancer that is only in cells in the lining of the bladder is called superficial bladder cancer. The doctor might call it carcinoma in situ, which is cancer that involves only the cells in which it began – and that has not spread to neighboring tissues. This type of bladder cancer often comes back after treatment. If this happens, the disease most often recurs as another superficial cancer in the bladder.

Cancer that begins as a superficial tumor may grow through the lining and into the muscular wall of the bladder. This is known as invasive cancer. Invasive cancer may extend through the bladder wall. It may grow into a nearby organ such as the uterus or vagina (in women) or the prostate gland (in men). It also may invade the wall of the abdomen.

When bladder cancer spreads outside the bladder, cancer cells are often found in nearby lymph nodes. If the cancer has reached these nodes, cancer cells may have spread to other lymph nodes or other organs, such as the lungs, liver, or bones.

When cancer spreads or metastasizes from its original place to another part of the body, the new tumor has the same kind of abnormal cells and the same name as the primary tumor. For example, if bladder cancer spreads to the lungs, the cancer cells in the lungs are actually bladder cancer cells. The disease is metastatic bladder cancer, not lung cancer. It is treated as bladder cancer, not as lung cancer. Doctors sometimes call the new tumor “distant” disease.