The causes of cancer of the large bowel

In the UK, approximately 36,000 people each year develop cancer of the large bowel. In most people the cause of cancer of the large bowel is still unknown, but research is going on all the time to try to find the cause. Like most types of cancer, bowel cancer is more common in older people. It is unusual for bowel cancer to be diagnosed in people under 50.

Diet

Research suggests that cancer of the large bowel may be linked to diet. It is thought that a diet high in animal fat and protein, and low in fibre (fruit and vegetables), may increase the risk of developing cancer of the bowel.

Inherited faulty genes

A person who has one or more family members with bowel cancer may have a higher risk of developing the disease. They are usually only at higher risk if bowel cancer has been diagnosed in a close family member (such as a parent, or sister or brother) under the age of 45 years, or when there is bowel cancer in several close members of the same family.

People who are worried about bowel cancer because of their family history can be referred to specialist clinics where their risk will be carefully assessed. Regular screening, usually with a colonoscopy, can be arranged for people who have a high risk of developing the disease. Contact your GP or CancerBACUP’s Cancer Support Service for more information. You can also read CancerBACUP’s section on cancer genetics.

There are two rare genetic conditions in which people have a high risk of developing bowel cancer. In Familial Adenomatous Polyposis (FAP), numerous benign tumours called polyps are found in the lining of the colon. People with FAP have a high risk of developing bowel cancer. In another inherited genetic condition known as Hereditary Non-Polyposis Colon Cancer (HNPCC), bowel cancers develop at an early age, sometimes in more than one place in the bowel.

Bowel diseases

People who have had ulcerative colitis or Crohn’s disease for a long time also have an increased risk of developing bowel cancer during their lifetime. Ulcerative colitis and Crohn’s disease are diseases of the lining of the bowel.