We still do not know exactly what causes most bladder cancers. But researchers have found some risk factors and are making progress toward understanding how these factors cause cells in the bladder to become cancerous. (See the section, "What are the risk factors for bladder cancer?")

During the past few years, scientists have made a lot of progress in understanding how certain changes in DNA can cause normal bladder cells to grow abnormally and form cancers. DNA is the genetic material that carries the instructions for nearly everything our cells do.

We usually resemble our parents because they passed their DNA on to us. However, DNA affects more than our outward appearance. Some genes (parts of our DNA) contain instructions for controlling when cells grow and divide. Certain genes that promote cell division are called oncogenes. Others that slow down cell division or cause cells to die at the appropriate time are called tumor suppressor genes.

Cancers can be caused by DNA mutations (defects) that activate (turn on) oncogenes or inactivate (turn off) tumor suppressor genes. Some people inherit DNA mutations from their parents that greatly increase their risk for developing breast, ovarian, colorectal and several other cancers. However, bladder cancer does not often run in families, and inherited gene mutations presently are not believed to be a major cause of this disease.

DNA mutations related to bladder cancer usually develop over a lifetime rather than having been inherited before birth. Every time a cell prepares to divide into 2 new cells, it must duplicate its DNA. This process is not perfect and copying errors in the DNA can occur. Fortunately, cells have repair enzymes that proofread DNA. But some errors may slip past, especially if the cells are growing rapidly.

Acquired DNA mutations may result from exposure to cancer-causing chemicals in tobacco smoke that are absorbed into the blood, filtered by the kidneys and released into the urine. Acquired changes in genes, such as the p53 or Rb1 tumor suppressor genes and the HER-2/neu oncogene, are thought to be important in the development of bladder cancer. Changes of these and similar genes may also be responsible for making some bladder cancers more likely to grow and invade more rapidly than others. Current research in this field is aimed at developing tests that can find bladder cancers at an early stage by recognizing their DNA changes.

Although bladder cancers do not often result from inherited mutations in oncogenes or tumor suppressor genes, some people seem to inherit a reduced ability to detoxify (break down) certain types of cancer-causing chemicals. These people are more sensitive to the cancer causing effects of tobacco smoke and certain industrial chemicals. Researchers are developing tests that may help identify such people, but these tests are not routinely available. It is not certain how these test results would be used since doctors recommend that all people avoid tobacco smoke and hazardous industrial chemicals.

Last Medical Review: 01/27/2009
Last Revised: 5/13/2009