A screening test is used to look for a disease when a person doesn’t have symptoms. Colorectal cancer almost always develops from precancerous polyps (abnormal growths) in the colon or rectum. Screening tests can find precancerous polyps, so that they can be removed before they turn into cancer. Screening tests can also find colorectal cancer early, when treatment works best. Regular screenings beginning at age 50 is the key to preventing colorectal cancer.