We do not know exactly what causes most bladder cancers. Certain changes in the DNA inside normal bladder cells can make them grow abnormally and form cancers. DNA is the chemical in each of our cells that makes up our genes – the instructions for how our cells function. We usually look like our parents because they are the source of our DNA, but DNA affects more than just how we look.
Some genes control when cells grow, divide into new cells, and die. Genes that help cells grow, divide, and stay alive are called oncogenes. Genes that slow down cell division or cause cells to die at the right time are called tumor suppressor genes. Cancers can be caused by DNA changes that turn on oncogenes or turn off tumor suppressor genes. Several different gene changes are usually needed for a cell to become cancerous.
Some people inherit DNA changes (mutations) from their parents that increase their risk for developing certain cancers. But bladder cancer does not often run in families, and inherited gene mutations are not thought to be a major cause of this disease.
DNA changes related to bladder cancer usually develop during a person’s life rather than having been inherited before birth. Some of these acquired DNA mutations result from exposure to cancer-causing chemicals or radiation. For example, chemicals in tobacco smoke can be absorbed into the blood, filtered by the kidneys, and end up the urine, where they can affect bladder cells. Other chemicals may reach the bladder in a similar way. But in some cases, gene changes may just be random events that sometimes happen inside a cell, without having an outside cause.
Bladder cancers are not usually caused by inherited mutations in oncogenes or tumor suppressor genes, but some people seem to inherit a reduced ability to detoxify (break down) and get rid of 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 to identify such people, but these tests are not routinely done. It is not certain how these test results would be used since doctors recommend that all people avoid tobacco smoke and hazardous industrial chemicals.