Causes and risk factors of colon and rectal cancer
Each year in the UK, approximately 25,500 people develop cancer of the colon, and about 14,000 people develop cancer of the rectum. The cause of both conditions in most people is still unknown, but research is going on to try to find out more.
Like most types of cancer, colon and rectal cancer are more common in older people – more than 80% of (8 in 10) bowel cancers (cancers of the colon and rectum) are diagnosed in people over 60.
There’s evidence that a diet containing a lot of red and processed meats (such as smoked meat, ham, bacon, sausages, pâté and tinned meat) can increase the risk of developing cancer of the bowel. Eating fried or grilled meat might also increase the risk. The greatest increase in risk seems to be for people who eat two or more portions of red or processed meat a day. People who eat less than two portions a week seem to have the lowest risk. No link has been found between eating poultry (such as turkey and chicken) and an increased risk of bowel cancer.
Eating a diet low in fruit and fresh vegetables may also increase a person’s risk. It’s not clear whether eating certain types of fat increases the risk of developing bowel cancer.
Cancer of the colon and rectum may be more common in people who get very little exercise and who are overweight. It’s also more common in people who follow a low-fibre diet and people who have smoked cigarettes for many years. A high alcohol intake also increases the risk.
A person with one or more family members with bowel cancer may have a higher risk of developing it. The risk is usually only higher if bowel cancer has been diagnosed in a close family member (such as a parent, sister or brother) under the age of 45, or when several close members on the same side of a family have all had bowel cancer.
People who are worried about bowel cancer because of their family history can be referred to a specialist clinic. At the clinic their risk will be carefully assessed. Regular screening, usually with a colonoscopy (a test to look at the inside of all of the large bowel), can be arranged for people with a high risk. Contact your GP for more information.
Only about 5% of (5 in every 100) colon and rectal cancers are caused by an inherited faulty gene.
There are two rare conditions that can run in families: familial adenomatous polyposis (FAP) and hereditary non-polyposis colon cancer (HNPCC). People with either condition have a very high risk of developing colon cancer.
Familial adenomatous polyposis (FAP)
People with FAP have many hundreds or thousands of benign tumours (polyps) in the lining of the colon and rectum. They will be regularly screened using a colonoscopy or sigmoidoscopy (a test to look at the inside of the rectum and the sigmoid colon) to look for signs of cancer. Usually, it’s recommended that people with FAP have an operation to remove their bowel.
Unless the bowel is removed, nearly everyone with FAP will develop bowel cancer. FAP causes about 1% of (1 in every 100) bowel cancers.
Hereditary non-polyposis colon cancer (HNPCC)
People with HNPCC have an increased risk of developing bowel cancers at a young age, sometimes in more than one place in the bowel. Unlike FAP, people with HNPCC have very few polyps in the bowel. If you have HNPCC, you’re likely to be screened every couple of years using a colonoscopy. Screening usually starts from the age of 25, or five years before the age when your youngest relative developed bowel cancer. HNPCC causes about 3% of (3 in every 100) bowel cancers.
We have further information about FAP and HNPCC.
Personal history of inflammatory bowel diseases
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People who’ve had ulcerative colitis or Crohn’s disease (diseases of the lining of the bowel) for a long time also have an increased risk of developing bowel cancer. Irritable bowel syndrome is not an inflammatory bowel disease and doesn’t increase your risk of developing bowel cancer.
Bowel cancer is not infectious and can’t be passed on to other people.
We have information that might be helpful if you are concerned about a genetic risk of bowel cancer, or you could talk to us.