Colonoscopy is the most accurate test for cancer of the colon and rectum, proven to detect the disease early and save lives. Health care providers can spot and remove polyps during a colonoscopy, which uses a flexible, lighted tube to examine the colon and rectum. if necessary, polyps or other types of abnormal tissue can be removed through the scope during a colonoscopy. Tissue samples (biopsies) can be taken during a colonoscopy as well.