May 10, 2011
2 min read

Flexible sigmoidoscopy more likely to miss colorectal tumors vs. colonoscopy in elderly

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Digestive Disease Week 2011

CHICAGO — Flexible sigmoidoscopy was four times more likely to miss cancer in the distal colon in patients aged 67 or older, according to results from a study of more than 28,000 patients.

Although colonoscopy has its limitations, Yize Richard Wang, MD, PhD, recommended colonoscopy over sigmoidoscopy for older patients.

“We were surprised that when we compared the rate of interval cancer only for the distal colon, it was 2.6% for colonoscopy but four times as high for sigmoidoscopy, at 11.7%,” he said. “Despite the imperfections of colonoscopy, it remains the preferred procedure for detecting colon cancer, and for colon cancer prevention.”

Wang, a gastrointestinal fellow at Mayo Clinic Florida, discussed the results during a Tuesday press conference at Digestive Disease Week 2011.

All patients in the study, selected from the SEER database, were aged 67 or older and underwent their first colonoscopy from January 1998 to December 2002, and were subsequently diagnosed with colorectal cancer within 36 months. Cancers diagnosed within 6 months of colonoscopy were categorized as detected cancers and those diagnosed 6 to 36 months after colonoscopy were categorized as interval cancers.

Medicare HMO enrollees or those without Part B coverage in the 24 months prior to colonoscopy were excluded. Researchers also excluded high-risk patients with inflammatory bowel disease, family history of gastrointestinal malignancy or personal history of colonic polyps.

There were 30,483 patients included in the study; 93.1% of cancers were detected and 6.9% were interval. There were 3,523 sigmoidoscopies and 57,412 colonoscopies performed.

The rate of new or missed colorectal cancers was 4% after colonoscopy vs. 12% after sigmoidoscopy. The rate of interval cancer was higher among patients older than 80 years (8.1%) vs. those aged 67 to 80 years (6.2%).

In the left-side colon, the risk for new or missed cancers was again four times higher with sigmoidoscopy (OR=4.02; 95% CI, 3.53-4.38). The interval cancer rate was also higher in colonoscopies performed by non-gastroenterologists compared with gastroenterologists: 7.5% vs. 6.6%. – by Jason Harris

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When you're looking for a cancer or a polyp, the further you look the better. Sigmoidoscopy has gotten a bad name because patients are not well-prepared - the procedure is done without sedation and patients may only get an enema or two. With colonoscopy, patients are very well-prepared and sedated, and we can go far up the colon. With sigmoidoscopy, you never know how far you've gotten because the landmarks aren't there that we use for colonoscopy. If you're going to look for bright red rectal bleeding and just evaluating the rectum and lower sigmoid colon, sigmoidoscopy is fine. As a screening procedure, it's not very good.

– Jerome D. Waye, MD
Clinical Professor of Medicine, Mount Sinai Medical Center

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