Diagnosis

Screening tests play a key role in detecting polyps before they become cancerous. These tests can also help find colorectal cancer in its early stages, when you have a good chance of recovery.

Screening methods include:

• Colonoscopy, the most sensitive test for colorectal polyps and cancer. If polyps are found, your doctor may remove them immediately or take tissue samples (biopsies) for analysis.
• Virtual colonoscopy (CT colonography), a minimally invasive test that uses a CT scan to view your colon. Virtual colonoscopy requires the same bowel preparation as a colonoscopy. If a polyp is found during the CT scan, you'll need to repeat the bowel preparation for a colonoscopy to have the polyp examined and removed.
• Flexible sigmoidoscopy, in which a slender tube with a light and camera is inserted into your rectum to examine the last third of your colon (sigmoid) and rectum. The majority of the colon is not examined with this screening test, so some polyps and cancers may not be discovered.
• Stool-based tests. This type of test works by checking for the presence of blood in the stool or assessing your stool DNA for evidence of a colon polyp or cancer. If your stool test is positive you will need a colonoscopy soon afterward.