Why should you get a screening? Colorectal cancer is the #2 cancer killer in the U.S. A screening test is used to look for a disease when a person doesn’t have symptoms. Colorectal cancer (colon cancer) almost always develops from precancerous polyps (abnormal growths) in the colon or rectum. A screening test can help find precancerous polyps, so that they can be removed before they turn into cancer. There is also a chance to detect cancer early, when treatment tends to work