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In a large study of older adults, the risk of new or missed left-sided colorectal cancers (CRCs) jumped from 4% after colonoscopy to 12% after flexible sigmoidoscopy.

This quadrupling of the new/missed CRC rate was noted by Yize Richard Wang, MD, PhD, of the Mayo Clinic in Jacksonville, Florida, and collaborators. In research presented at the Digestive Disease Week conference, held May 7-10, 2011, in Chicago, Illinois, the investigators examined data from all patients in the Surveillance, Epidemiology, and End Results Medicare (SEER-Medicare) who were at least 67 years old when undergoing a lower endoscopy from 1998 to 2005 and who were subsequently diagnosed with CRC within 3 years.

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After excluding high-risk patients with preexisting inflammatory bowel disease, family history of GI malignancy, or personal history of colonic polyps, Yang and colleagues included 52,236 men and women in the study. Among them, 3,523 flexible sigmoidoscopies and 57,412 colonoscopies were performed within 36 months prior to CRC diagnosis.

• Detected CRCs were defined as those diagnosed within 6 months after a lower endoscopy.

• New or missed CRCs were defined as those diagnosed 6 to 36 months after a lower endoscopy.

For flexible sigmoidoscopy, the study sample was limited to left-sided CRCs distal to the splenic flexure. Within the 12% rate of new or missed left-sided CRCs recorded after flexible sigmoidoscopy, the highest rate was seen in the descending colon.

The 4% rate of new or missed CRCs after colonoscopy increased from 2% to 3% in the left-sided colon and 5% to 6% in the right-sided colon.

“Among older patients, the risk of new or missed left-sided CRCs quadrupled after flexible sigmoidoscopy compared with colonoscopy,” stated the authors, and suggested that further research is needed to determine whether bowel preparation or endoscopist attributes were factors. ONA