Causes of bladder cancer

Bladder cancer is caused by changes to the cells of the bladder. It's often linked with exposure to certain chemicals, but the cause isn't always known.

What is cancer?

Cancer begins with a change (mutation)in the structure of the DNA in cells, whichcanaffect how they grow. This means that cells grow and reproduce uncontrollably, producing a lump of tissue called a tumour.

Increased risk

Severalfactorshave been identified that can significantly increase your risk of developing bladder cancer.

Smoking

Smoking is the single biggest risk factor for bladder cancer. This is because tobacco contains cancer-causing (carcinogenic) chemicals.

If you smoke for many years, these chemicals pass into your bloodstream and are filtered by the kidneysinto your urine. The bladder is repeatedly exposed to these harmful chemicals, as it acts as a store for urine. This can cause changes to the cells of the bladder lining, which maylead to bladder cancer.

It's estimated thatjust over a thirdof all cases of bladder cancer are caused bysmoking. People who smoke may be up tofour times more likely to develop bladder cancer than non-smokers.

Exposure to chemicals

Exposure to certain industrial chemicals is the second biggest risk factor. Previous studies have estimated that this may account for around 25% of cases.

Chemicals known to increase the risk of bladder cancer include:

• aniline dyes
• 2-Naphthylamine
• 4-Aminobiphenyl
• xenylamine
• benzidine
• o-toluidine

Occupationslinked to an increased risk of bladder cancer are manufacturing jobs involving:

• dyes
• textiles
• rubbers
• paints
• plastics
• leather tanning

Some non-manufacturing jobs have also been linked to an increased risk of bladder cancer. These include taxi or bus drivers, as a result of their regular exposure to the chemicals present in diesel fumes.

The link between bladder cancer and these types of occupations was discovered in the 1950s and 1960s. Since then, regulations relating to exposure to cancer-causing chemicals have been made much more rigorous and many of the chemicals listed abovehave been banned.

However,these chemicals are stilllinked with cases of bladder cancer now, as it can take up to30 years after initial exposure to the chemicals before the condition starts to develop.

Other risk factors

Otherfactors that can increase your risk of bladder cancer include:

• Radiotherapy to treat previous cancers near the bladder, such as bowel cancer
• previous treatment withcertain chemotherapy medications, such ascyclophosphamide and cisplatin
• previous surgery to remove part of the prostate gland, during treatment for benign prostate enlargement
• having diabetes bladder cancer is thought to be linked to certain treatments for type 2 diabetes
• having a tube in your bladder (an indwelling catheter) for a long time, because you have nerve damage that has resulted in paralysis
• long-term or repeated urinary tract infections (UTIs)
• long-term bladder stones
• having an early menopause (before the age of 42)
• an untreated infection called schistosomiasis , which iscaused by a parasite thatlives in fresh waterthis is very rare in the UK

How does bladder cancer spread?

Bladder cancer usually begins in the cells of the bladder lining. In some cases, itmay spread into surrounding bladder muscle. If the cancer penetrates this muscle, itcan spread to other parts of the body, usually through the lymphatic system.

If bladder cancer spreads to other parts of the body, such as other organs, it's known as metastatic bladder cancer.