The bladder is a hollow, muscular, balloon-like organ that stores urine. It sits in the lower part of the abdomen. Urine consists of water and waste products not needed by the body.
The bladder is lined with a membrane that stops the urine going into the body. The cells of this membrane are called transitional cells or urothelial cells. The membrane lining is called the urothelium.
The kidneys produce urine, which is carried to the bladder by tubes called ureters. The bladder stores the urine. When it is full enough, urine is passed from the body through a tube called the urethra.
In women, the urethra is a very short tube in front of the vagina (birth canal). In men, the tube is longer and passes through the prostate and the penis.
Nearly all cancers of the bladder begin in the urothelium (lining of the bladder). These are called urothelial (or transitional cell cancers). They come in a wide range of forms and can behave in very different ways. Transitional cell cancers grow from the inside lining of the bladder. They are either superficial or invasive cancers.
Most bladder cancers are superficial cancers. They either look flat and red (carcinoma in situ) or stick out from the lining like mushrooms (papillary). Superficial cancers don't often spread to other parts of the body.
Less often, transitional cell cancers grow deeply into the wall of the bladder. These are called invasive cancers and are more likely to spread to other parts of the body.
The exact causes of bladder cancer are not clearly understood. However, some risk factors make it more likely that a person will develop bladder cancer.
Cigarette smoking is the most important factor. Some chemicals found in cigarette smoke can cause bladder cancer.
The chemotherapy drug called cyclophosphamide can increase the long-term risk of bladder cancer.
Another known risk factor for bladder cancer is exposure to certain chemicals at work. They include chemicals used in dyeing in the textile, petrochemical and rubber industries. Bladder cancer may develop many years after exposure to these chemicals. It is difficult to prove that exposure to chemicals at work definitely caused a particular person's bladder cancer.
Chronic inflammation of the bladder has been linked to squamous cell carcinoma of the bladder.
In Egypt and Asia, infection with the parasite schistosoma (bilharzia) is associated with bladder cancer.
Bladder cancer occurs most commonly from the age of 55 and is three times as common in men as in women.
Reviewed by: Dr Farshad Foroudi, Radiation Oncologist, Peter MacCallum Cancer Centre; Dr Mario Guerrieri, Radiation Oncologist, Radiation Oncology Victoria; Mr Shomik Sengupta, Urologist, Freemason's Medical Centre