Colonoscopy May Reduce Late-Stage Colon Cancer Risk by 70%

Jenni Laidman

March 04, 2013

Colonoscopy is associated with a 70% reduced risk for late-stage colorectal cancer (CRC) among people of average risk, and sigmoidoscopy is associated with reduced risk for cancers of the left colon, according to a study published online March 4 in the Annals of Internal Medicine.

Chyke A. Doubeni, MD, MPH, associate professor of family medicine and community health, Perelman School of Medicine, University of Pennsylvania, and colleagues compared the CRC screening histories of 471 patients who were aged 55 to 85 years from 2006 through 2008 and who were diagnosed with late-stage (IIB or higher) colorectal cancer with the screening histories of 509 matched control patients without cancer. Both case and control patients were enrolled in 1 of 4 managed-care plans for 5 years or longer. Anyone with a strong family history of CRC, a past total colectomy, or a history of inflammatory bowel disease was excluded from the study.

"This shows what the people who do screening on a daily basis already know," John R. Saltzman, MD, director of endoscopy, Brigham and Women's Hospital, Boston, Massachusetts, told Medscape Medical News. Dr. Saltzman has no connection with the current study. "Sigmoidoscopy is protective only on the left side, where it reaches. The only thing that is surprising to me is that several prior studies that attempted to look at this have not shown this. I'm glad to see a study that sort of confirms what we know."

Colonoscopy screening was associated with an adjusted odds ratio (AOR) for any late-stage CRC of 0.29 (95% confidence interval [CI], 0.15 - 0.58). Sigmoidoscopy corresponded with an AOR of 0.50 (95% CI, 0.36 - 0.70). For cancer of the right colon, colonoscopy corresponded with an AOR of 0.36 (95% CI, 0.16 - 0.80), and sigmoidoscopy with a nonsignificant AOR of 0.79 (95% CI, 0.51 - 1.23). For the left colon and rectum, the investigators found no statistically significant AORs for either colonoscopy or sigmoidoscopy.

Previous studies have shown that cancer of the right colon accounts for half of all colon cancer diagnoses in the United States.

The results in this study were adjusted for birth year, duration of enrollment in the health plan, receipt of other screening tests (such as fecal occult blood tests), comorbidities, number of preventive healthcare visits 5 years before the reference period, socioeconomic status, and family history of CRC.

Because screening colonoscopy was relatively uncommon during the study period, study precision was limited by the low number of participants, the authors note. Thirteen (2.8%) of the case patients and 46 (9.0%) of the control patients underwent screening colonoscopy; 92 (19.5%) case patients and 173 (34.0%) control patients were screened via sigmoidoscopy.

"The biggest concern, and the biggest surprise to me, was the very low rate of screening in both [case and control] groups," Duardo Brooks, MD, MPH, told Medscape Medical News. Dr. Brooks, director of prostate and colorectal cancers for the American Cancer Society, has no association with the study.

"It's important to point out that this was an insured population. It's a huge disappointment, in that we know colon screening by any recommended measure potentially reduces the risk of dying and decreases the risk of advanced disease and prevents disease," Dr. Brooks said.

This study was supported by a grant from the National Cancer Institute. Various authors report receiving funding from or other financial relationships with Kaiser Permanente, Hawaii; the National Cancer Institute; the National Institutes of Health; the Centers for Disease Control and Prevention; Verisk Health; the Commonwealth Foundation; the American Gastroenterological Association; the International Society for Diseases of the Esophagus; UpToDate; the Canadian Medical Association Journal Oversight Committee. Dr. Doubeni, Dr. Saltzman, and Dr. Brooks have disclosed no relevant financial relationships.

Ann Intern Med. Published online March 4, 2013.

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