Causes and risk factors of bowel cancer

In the UK, about 41,000 people get cancer in the large bowel each year. The large bowel includes the colon and the rectum.

The exact cause of bowel cancer is unknown. But, things called risk factors can increase the chance of a person developing it. Having one or more risk factors does not mean you will definitely get bowel cancer. And if you do not have any risk factors, it does not mean you will not get bowel cancer.

If you are worried about bowel cancer and would like to talk to someone, we're here. You can:

• Call the Macmillan Support Line on 0808 808 00 00.
• Chat to our specialists online.

Eating a lot of red and processed meat increases the risk of bowel cancer.

Red meat includes:

• beef
• lamb
• pork
• veal
• venison
• goat.

Processed meat includes:

• smoked meat
• ham
• bacon
• sausages
• pate
• tinned meat.

Eating fried or grilled meat may also increase the risk.

Current UK guidelines recommend that you eat no more than 70g of red meat per day. That is about 3 slices of ham or 1 lamb chop. No link has been found between bowel cancer and eating poultry such as chicken and turkey, or seafood.

Not eating enough fruit and fresh vegetables may also increase the risk.

Being overweight can increase the risk of developing bowel cancer, especially in men.

Having an inflammatory bowel condition, such as ulcerative colitis or Crohn’s disease, can increase the risk of bowel cancer.

People with these conditions may be offered regular bowel screening with a test called a colonoscopy.

Irritable bowel syndrome is not an inflammatory bowel condition. It does not increase the risk of getting bowel cancer.

Most people who get bowel cancer do not have a family history of it. Having one family member who developed bowel cancer at an older age does not increase your risk.

If several close family members on the same side of your family have had bowel cancer, this may increase your risk. You may also have a higher risk if a close family member had bowel cancer before the age of 50. Close family members are parents, brothers and sisters.

People who have a history of bowel cancer in their family can be referred to a specialist clinic to have their risk assessed. People at higher risk of bowel cancer are offered bowel screening with a colonoscopy. For more information, contact your GP or call our cancer support specialists on 0808 808 00 00.

About 5 in every 100 bowel cancers (5%) are caused by an inherited faulty gene.

There are two rare conditions that can run in families:

• familial adenomatous polyposis (FAP)
• Lynch syndrome (also called hereditary non-polyposis colorectal cancer or HNPCC).

People with either condition have a very high risk of developing bowel cancer.

We have information about cancer and genetics.

Bowel cancer is not infectious and cannot be passed on to other people.

Familial adenomatous polyposis (FAP)

FAP causes less than 1 in every 100 bowel cancers (less than 1%).

People with FAP have hundreds or thousands of benign tumours (polyps) in the lining of their colon. They may also have polyps in their rectum.

People with FAP have regular screening using colonoscopies to look for signs of cancer. It is usually recommended that people with FAP have an operation to remove their colon and sometimes their rectum. Unless the colon is removed, nearly everyone with FAP will develop bowel cancer.

Lynch syndrome (HNPCC)

People with Lynch syndrome have an increased risk of developing bowel cancer at a young age. Lynch syndrome causes about 4 in every 100 bowel cancers (4%).

If you have Lynch syndrome, you will usually have regular screening using colonoscopies. Screening normally starts from the age of 25. Or it may start five years before the age at which your youngest relative developed bowel cancer. The colonoscopy is usually repeated every 18 months to 2 years..