Colorectal cancer is cancer that begins in the colon or rectum (everyone has a colon and rectum unless they have been surgically removed). This cancer can be prevented with a screening colonoscopy by removing polyps (grape-like growths on the wall of the large intestine, which includes both the colon and rectum) before they become cancerous. With routine screening using visual or stool-based tests, you can also detect the disease early when the cancer is small and hasn’t spread.