How do bowel cancers develop?

Bowel cancers may arise from benign adenomatous polyps in the large bowel. These polyps are growths on little stalks on the wall of the large bowel. They can be tiny (a few millimetres across) or quite large (up to 3 centimetres across). They can often be completely removed at colonoscopy. Having a lot of large adenomatous polyps is a risk factor for developing bowel cancer. The risk of a polyp turning cancerous increases with the size of the polyp. A person who has this problem will have regular colonoscopies to remove these polyps at an early stage to prevent bowel cancer.

Diagram of the colon showing polyps growing from the wall of the bowel into the lumen. The inset picture shows a typical polyp on a stalk as viewed through a colonoscope. (Courtesy of the artist Therese Winslow)

Amended February 2009