Bladder cancer risks and causes

A risk factor is anything that can increase your chance of developing cancer. Different cancers have different risk factors.

Remember that having one or more risk factors does not mean that you will definitely get bladder cancer. Many people who have one or more of the risk factors never get bladder cancer and some people who have none of the risk factors do develop bladder cancer. Risk factors are only a guide to what may increase risk.

More than 10,500 people are diagnosed with bladder cancer each year in the UK. Not counting non melanoma skin cancer, bladder cancer is the 7th commonest cancer in the UK.  It is the 4th commonest cancer for men and the 12th most common for women.

More men than women get bladder cancer. This may just be because more men than women have smoked in the past few decades. And more men have been exposed to chemicals at work.

Your ethnic background is also related to your risk. Black men have about half the risk of bladder cancer of white men. Black women have about two thirds the risk of white women. Risk in Asian men and women is even lower.

Bladder cancer usually takes a long time to develop and it is most common in older people. Most people with bladder cancer are between 50 and 80 years old. It is rare in people under 40.

Smoking cigarettes definitely increases the risk of bladder cancer. Your risk if you smoke is up to 6 times that of a non smoker. People with the highest risk are those who smoke heavily, or started smoking at a young age, or have smoked for a long time. Smoking cigars and pipes also increases bladder cancer risk. In the UK,  a large Cancer Research UK study in 2010 looking at lifestyle factors found that just over a third of all bladder cancers are caused by smoking. 

The chemicals in the smoke get into the bloodstream. They are then filtered out of the blood by the kidneys and end up in the urine. When the urine is stored in the bladder, these chemicals are in contact with the bladder lining. Chemicals called arylamines in cigarette smoke may be the cause of the increased bladder cancer risk in smokers. In people who smoke, passing urine more frequently (especially at night) may reduce bladder cancer risk. 

Some research suggests that exposure to secondhand smoke (passive smoking) in childhood may increase bladder cancer risk.

A group of chemicals called arylamines are known to cause bladder cancer. These chemicals have been banned in the UK for about 20 years. But it can take up to 25 years for a bladder cancer to develop. You may have been exposed to them a long time ago if you work in industries such as rubber or plastics manufacture. Arylamines that increase risk of bladder cancer include

• Aniline dyes
• 2-Naphthylamine
• 4-Aminobiphenyl
• Xenylamine
• Benzidine
• O-toluidine

Another group of chemicals called polycyclic hydrocarbons increase the risk of bladder cancer. Exposure to these chemicals is possible in industries where people handle carbon or crude oil, or substances made from them. You may also come into contact with them in any industry involving combustion, such as smelting.

If you have a diagnosis of bladder cancer, it is worth finding out if you have ever been exposed to any of these chemicals. If you have, talk to your urologist or cancer doctor. You may be able to claim an allowance called 'Industrial Disease Benefit' from the government Department for Work and Pensions.

Some other jobs have been linked to an increased risk of bladder cancer. These include

• Bus and taxi drivers
• Metal casters, machine setters and operators
• Leather workers
• Blacksmiths
• Hairdressers
• Mechanics
• Miners
• Painters

In all these occupations the increase in risk of bladder cancer is less than 30%.

When chlorine is used to disinfect water it can break down into chemicals called trihalomethanes (THMs). Chlorine is used to disinfect drinking water and swimming pools. It stops the growth of bacteria that can harm us. Some studies have looked at whether exposure to THMs by drinking chlorinated water can increase bladder cancer risk. Some studies seem to show that long term drinking of tap water with high levels of THMs may increase the risk of bladder cancer but findings are mixed. Other studies have shown a reduced risk of bladder cancer in people who drink a lot of water, especially if they empty their bladder often.

Swimming in, or bathing or showering in, chlorinated water can also increase the risk when the chemicals are absorbed through the skin or breathed in as water droplets. But it is important to remember that disinfecting water reduces the risk of serious infectious diseases, so the risk of not chlorinating water is likely to be higher than that of exposure to THMs.

Treatment with radiotherapy to the pelvic area for cancers such as cervical cancer, prostate cancer, fallopian tube cancer, testicular cancer and womb cancer can increase your risk of bladder cancer. And treatment with the chemotherapy drugs cyclophosphamide and cisplatin also increases the risk.

Men who have had surgery to remove part of their prostate gland as a treatment for non cancerous (benign) overgrowth of the prostate have up to a 50% increase in their risk of bladder cancer. Researchers think that the increased risk is related to the benign overgrowth of the prostate gland rather than the surgery though.

People who have type 2 diabetes have a 40% increase in their risk of developing bladder cancer.

Some studies in the past have seemed to show that if you have had many bladder infections, or suffer from chronic bladder infection, you may be more at risk of bladder cancer. The risk is particularly high for a type called squamous cell cancer of the bladder. But one recent study did not find an increase in risk for people with a history of common bladder infections and one study actually showed a decrease in risk in women. So we need more research to find out if there is a link between bladder infections and bladder cancer.

Smokers who have repeated bladder infections may have a much higher risk, with one study reporting a risk 10 times higher than the general population.  Recent studies have found that men who have had gonorrhoea infection also have an increased risk of bladder cancer.

In the developing world, parasitic infection is the main cause of bladder cancer. A parasite called bilharzia or schistosomiasis is widespread in many countries and increases the risk of squamous cell bladder cancer. But in the UK, parasitic infection is extremely rare and infection is a much less common cause of bladder cancer than smoking or workplace chemicals.

Bladder stones are little lumps of calcium that can form in the urinary system. You can get kidney or bladder stones. If you have stones in the bladder (sometimes called bladder calculi), you may be more at risk from a type of bladder cancer called squamous cell bladder cancer. This is because stones can cause chronic infection. But you would need to suffer from this for a long time before it would increase your risk of bladder cancer.

A healthy diet may lower your risk of bladder cancer. Some studies seem to show that eating as little as 100 grams of fruit a day (about 4 ounces) can significantly lower your bladder cancer risk, but some other studies show no reduction in risk. High beta-carotene levels in the diet have been shown in one study to reduce bladder cancer risk in people who smoke. Selenium is a nutrient found in various foods and has also been shown to protect against bladder cancer in some studies.

One study showed that vegetarians have half the risk of bladder cancer of non vegetarian people, but more studies are needed before we can be sure about this. Eating a lot of bacon was shown to increase bladder cancer in one study. But other studies have shown no bladder cancer risk in people who eat a lot of meat.

Many other foods have been studied but there is no clear evidence that any of them increase risk of bladder cancer.

One study has shown that people who drank large amounts of alcohol had a lower bladder cancer risk, especially if they passed urine often. But another study showed that drinking alcohol did not reduce risk, apart from beer. It is important to remember though that alcohol increases the risk of several other cancers, including breast and bowel cancer.

If you have already been successfully treated for a bladder cancer in the past then your risk of developing another cancer anywhere in the urinary tract is higher. This includes

• Any part of your bladder that is still there after your treatment
• The tubes that connect the kidney and the bladder (the ureters), including the part within the kidney (the renal pelvis)
• The tube leading from the bladder to the outside of the body (urethra)

For this reason your specialist will keep a close eye on you and you will have regular checkups to find any new cancer at its earliest stage. If you have had transitional cell cancer of other parts of the urinary tract (such as the ureters, urethra or renal pelvis) your risk of bladder cancer is also higher than other people in the population.

In a few families, bladder cancer is associated with an inherited faulty gene. But this is very rare. So even if someone in your family has bladder cancer, it is very unlikely that you have an increased risk yourself. If your relative was diagnosed before the age of 45, it is more likely that their cancer was caused by a gene fault. But family cancer patterns are influenced by behaviour too. Often cancers may seem to 'run in families' because of shared patterns of behaviour, such as smoking, which increase the risk of cancer. Overall, you are statistically more at risk if you have a first degree relative with bladder cancer (a parent, child, sister or brother). But remember, this is a statistical risk and can only tell you about risk in a whole population, not your risk as an individual person.

Two studies show that women who have an early menopause (before the age of 42 to 45) have their risk of bladder cancer increased by at least half compared to women who have their menopause at the age of 48 or later. The risk increases by the same amount in women who have both their ovaries removed for medical reasons.

As a baby develops inside the mother there is a connection between their bladder and belly button (umbilicus). This connection is called the urachus and usually disappears before the baby is born. The connection can remain after birth. This is extremely rare but can increase the risk of a rare type of bladder cancer called adenocarcinoma.

Another very rare birth defect called extrophy can also increase a person’s risk of developing bladder cancer later in life. Extrophy occurs when the bladder and urethra do not form properly. The bladder does not form its normal round shape but becomes flat and exposed to the outside of the body. It is turned 'inside out'. With the bladder outside the body and not protected by skin covering, it can easily become infected. This can eventually lead to adenocarcinoma of the bladder.

Some research has suggested that using hair dye may lead to an increased risk of bladder cancer, while other research has suggested it doesn’t. Some studies have probably been too small to show up any small increase in risk. In the Journal of the American Medical Association (JAMA) May 2005, a large meta analysis was published that looked into all the research on hair dyes causing cancer. This found that there is unlikely to be any link between dyeing your hair and bladder cancer.

In 2008, the WHO (World Health Organisation) said that there is some evidence that hair dyes can increase the risk of bladder cancer for male hairdressers and barbers. This is because they are working with these chemicals all the time. But this risk can be reduced by using non touch hairdressing techniques.

One research study has shown that people who have Down Syndrome have a lower risk of bladder cancer.

Most studies have shown no difference in risk of bladder cancer between people who are a normal weight and people who are overweight. But one recent American study showed that people who were overweight or obese were more at risk of developing bladder cancer.