Colonoscopy enables your physician to examine the lining of the colon for abnormalities. While the patient is under mild sedation, the physician inserts a flexible fiberoptic instrument called a colonoscope into the rectum and advances it through the colon (large bowel). Cancer can occur anywhere from the end of the colon (rectum) to the beginning of the colon, which is called the cecum. The colonoscope examines this entire area. Polyps and even small tumors can be removed painlessly at the time of a colonoscopy so it is really a "therapeutic," not just a "diagnostic" test.