Causes of bladder cancer
It's not always clear what causes bladder cancer. Bladder cancer has been linked to smoking, a parasitic infection, radiation and chemical exposure.
Bladder cancer develops when cells in the bladder begin to grow abnormally. Rather than grow and divide in an orderly way, these cells develop mutations that cause them to grow out of control and not die. These abnormal cells form a tumor.
We do not know exactly what causes most bladder cancers. But researchers have found some risk factors (see the section “What are the risk factors for bladder cancer?") and are starting to understand how they cause cells in the bladder to become cancerous.
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.
The gene changes that lead to bladder cancer are not the same in all cases. Acquired changes in certain genes, such as the TP53 or RB1 tumor suppressor genes and the FGFR and RAS oncogenes, are thought to be important in the development of some bladder cancers. Changes in these and similar genes may also make some bladder cancers more likely to grow and invade the bladder wall than others. Research in this field is aimed at developing tests that can find bladder cancers at an early stage by finding their DNA changes.
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.
Types of bladder cancer
Different types of cells in your bladder can become cancerous. The type of bladder cell where cancer begins determines the type of bladder cancer. Your bladder cancer type determines which treatments may work best for you. Types of bladder cancer include:
- Adenocarcinoma. Adenocarcinoma begins in cells that make up mucus-secreting glands in the bladder. Adenocarcinoma of the bladder is rare in the United States.
- Squamous cell carcinoma. Squamous cells appear in your bladder in response to infection and irritation. Over time they can become cancerous. Squamous cell bladder cancer is rare in the United States. It's more common in parts of the world where a certain parasitic infection (schistosomiasis) is a prevalent cause of bladder infections.
- Transitional cell carcinoma. Transitional cell carcinoma occurs in the cells that line the inside of your bladder. Transitional cells expand when your bladder is full and contract when your bladder is empty. These same cells line the inside of your ureters and your urethra, and tumors can form in those places as well. Transitional cell carcinoma is the most common type of bladder cancer in the United States.
Some bladder cancers include more than one type of cell.