What causes bladder cancer?

The ways in which bladder cancers develop and progress are only partly understood.  However, a number of substances that cause the cancers to develop have been identified.  Chief among them are cancer-causing agents in cigarette smoke and various industrial chemicals. Cigarette smoking alone has been estimated to cause 50 percent of all bladder cancer cases in the United States. Long-term workplace exposure to chemical compounds such as paints and solvents has been estimated to cause another 20 to 25 percent of bladder cancer cases. Carcinogens in the blood stream are filtered out by the kidneys to eliminate them from the body. However, these carcinogens remain in the bladder for a few hours interacting with the lining of the bladder before they are removed by urination. Through this process the bladder becomes a high risk organ for cancer, particularly in smokers.
More than 90 percent of all bladder cancers originate in the urothelium, the inner lining of the bladder. The majority of diagnosed bladder tumors are confined to the urothelium or the lamina propria and have not invaded the bladder muscle.