Any substance or condition that increases cancer risk is referred to as a risk factor. The most important risk factor for developing bladder cancer is smoking. However, most cancers are the result of many risk factors.
*Risk factors are generally listed in order from most significant to least significant. In most cases, it is impossible to rank the relative significance of individual risk factors with absolute certainty.
The risk of developing bladder cancer increases with age. It usually occurs in people over the age of 65 years. Men develop bladder cancer more often than women. Bladder cancer is more common in white people.
The following factors are known to increase the risk of developing bladder cancer.
Smoking
Tobacco smoking, particularly cigarette smoking, accounts for more than 50% of bladder cancers in men and approximately 40% of bladder cancers in women. Ex-smokers’ risk of developing bladder cancer is double that of people who have never smoked.
- Carcinogens that are found in tobacco smoke are also found in the urine of smokers. These include:
- aromatic amines – alpha naphthylamine and beta naphthylamine
- some cyclic N-nitrosomines
- arsenic
- These chemicals in the urine damage the cells that line the inside of the bladder (urothelial cells) which could lead to cancer.
- The risk of bladder cancer is associated with the number of cigarettes smoked per day, the number of years a person has smoked and the age at which a person started smoking.
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Occupational exposure to chemicals
Occupational exposure to chemicals is the second most important risk factor for bladder cancer. Exposure to aromatic amines (especially beta-naphythylamine, benzidine, 4-aminobiphenyl and 4-o-toluidine), polyaromatic hydrocarbons (PAHs) and diesel engine exhaust are most commonly found to increase the risk. Workers in the following industries could be at higher risk of developing bladder cancer:
- textiles
- rubber
- paint
- leather
- dye
- print
- metal
- machining
- plastics
- transportation
Examples of occupations that may increase the risk of developing bladder cancer include:
- bus or truck drivers
- painters
- mechanics
- miners
- machinists
- black smiths
- sheet metal workers
- printers
- foundry workers
- welders
- hair dressers
Smokers who are exposed to these chemicals in the workplace carry an even higher risk of developing bladder cancer.
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Chronic bladder irritation
Chronic bladder irritation increases the risk of bladder cancer. Chronic irritation can be caused by inflammation or trauma to the bladder.
Inflammation can be caused by:
- chronic urinary tract infection
- bladder stones
- schistosomiasis (bilharziasis) – an infection caused by a parasitic worm (Schistosoma haematobium) that usually occurs in developing countries
Trauma can be caused by:
- long-term indwelling catheters
- bladder stones
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Chemotherapy
People who have been treated for cancer with high doses of cyclophosphamide (Cytoxan, Procytox) or ifosfamide (Ifex) have an increased risk for bladder irritation which in turn increases the risk of developing bladder cancer. Increased fluid intake is important during treatment with these drugs. Sometimes protective drugs are given to reduce the risk of bladder irritation.
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Radiation therapy
People who have received radiation therapy to the abdomen or pelvis, or people who have survived atomic bombs and nuclear accidents, have an increased risk of bladder cancer.
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Arsenic
High levels of arsenic in drinking water increases the risk of bladder cancer.
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Personal history of urinary tract cancer
Having a cancer in any part of the urinary tract lining puts a person at higher risk of developing another tumour anywhere in the urinary tract, including the bladder.
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Bladder birth defects
Two rare birth defects, urachus and exstrophy, can increase a person's risk of developing bladder cancer:
- urachus
- The urachus is the connection between the navel (belly button) and the bladder that develops in a fetus.
- This connection usually disappears before a baby is born.
- If part of this connection remains after birth, it can become cancerous.
- exstrophy
- Exstrophy occurs when skin, muscle and connective tissue in front of the bladder do not close completely during fetal development, leaving a hole in the wall of the bladder.
- The inside of the bladder can be exposed to micro-organisms. This exposure can lead to chronic infections, which can increase the risk of bladder cancer.
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Aristolochic acids
Studies have shown that aristolochic acids, which are present in some types of plants, increase the risk of bladder cancer. People may be exposed to aristolochic acids through eating or drinking herbal products (including capsules, extracts, teas and dried herbs) that contain the plant species aristolochia or asarum. Aristolochic acids may be intentionally added to herbal products or accidently introduced as a contaminant. People who prepare or apply herbal products could also be exposed through direct contact with the plants.
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Possible risk factors
The following factors have some association with bladder cancer, but there is not enough evidence to say they are known risk factors. Further study is needed to clarify the role of these factors for bladder cancer.
- chlorine by-products
- People who drink chlorinated surface water (water from the surface of the earth such as a river, lake or reservoir) for most of their life have a slightly increased risk of bladder cancer.
- When chlorine is used to disinfect water, it can break down into chemicals called trihalomethanes (THMs) which could increase bladder cancer risk.
- genetics – There is no compelling evidence for a hereditary cause of bladder cancer. However, some studies have shown a connection between certain genes and the risk of bladder cancer.
- People with a mutation of the retinoblastoma (RB1) gene have a higher rate of bladder cancer. The RB1 gene mutation causes development of cancer in the eye during infancy.
- Studies have shown that people differ in the ability to break down chemicals and that this difference is determined by certain genes. Those who break down chemicals more slowly have an increased risk of developing bladder cancer.
- overuse of analgesics – There is inconsistent research regarding the use of analgesics (drugs that relieve pain). A number of studies have shown the heavy use of phenacetin can be linked to an increased risk of bladder cancer. However, other studies indicate an increased risk for renal pelvis cancer in the kidney, but nothing for the bladder.
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Unknown risk factors
The following are factors for which there is not enough evidence or the evidence is inconclusive. In other words, it can't be determined for sure whether these risk factors are or are not associated with bladder cancer.
- drinking too little fluid
- coffee
- artificial sweeteners
- alcohol
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See a list of questions to ask your doctor about risks. Find out how to reduce the risk of bladder cancer.