The majority of cancers in the large bowel (bowel or colorectal cancers) originate from growths called adenomas or polyps on the inner surface of the bowel. Bowel polyps are common, especially as people get older, and are usually not cancerous; however, a proportion do develop into cancer so they are generally removed when found. Bowel polyps are often found during a colonoscopy examination, which someone might have because they have symptoms that their doctor thinks should be investigated or because they have had a positive test result in a bowel cancer screening programme.
A colonoscopy involves a flexible tube with a camera attached being inserted into the rectum and through the bowel to examine the inside of the bowel. Sometimes, large (1cm or larger) or multiple polyps are found in the same individual. We know from previous research that people with large or multiple polyps are at higher risk of developing more polyps or bowel cancer in the future.
Risk groups based on findings during a colonoscopy examination:
- For people with 1 or 2 small polyps, their risk is classed as ‘low’. Current guidelines recommend that most people in the low risk group do not require a follow-up colonoscopy. A small number of people may require a follow-up colonoscopy after five years based on other factors such as their age, family history or other illnesses – this is called a surveillance colonoscopy.
- For people with 3 to 4 small polyps or 1 to 2 large polyps, their risk is classed as ‘intermediate’. Current guidelines recommend that everyone in the intermediate risk group is offered a follow-up colonoscopy after three years.
- For people with 5 or more small polyps or more than 3 polyps of which at least 1 is large, their risk is classed as ‘high’. Current guidelines recommend that everyone in the high-risk group is offered a follow-up colonoscopy after one year.
Surveillance colonoscopy is currently the standard way to monitor people at higher risk of bowel cancer. However, we know that significant disease will only be found in a small proportion of surveillance colonoscopies, which is important because colonoscopy also carries a small risk of complications for patients and is demanding on NHS resources.