Patients with familial adenomatous polyposis (FAP) have many hundreds of bowel polyps due to a genetic defect and are at very high risk of colorectal cancer. Many of them have the majority of the large bowel removed with only lowest part of the large bowel, the rectum, left and joined to the small bowel. The remaining rectum can still have up to 50 polyps and is regularly surveilled with sigmoidoscopy to see if any large polyps have grown so they can be removed before they turn into cancer. Some of these polyps are small and flat.