Negative Colonoscopy Associated with Low Colorectal Cancer Risk ►NCI Cancer Bulletin for September 6, 2011 - National Cancer Institute

Negative Colonoscopy Associated with Low Colorectal Cancer Risk

People who have no sign of cancer after a colonoscopy have a much lower risk of developing colorectal cancer over the next two decades than people who never had the procedure, according to a large case-control study conducted in Germany. Overall, people who had a negative colonoscopy were nearly 80 percent less likely to develop colorectal cancer than those who had never had a colonoscopy. The study was published online August 29 in the Journal of Clinical Oncology.
“Clearly, colonoscopy is not a preventive measure by itself. The strongly reduced risk among patients who underwent colonoscopy without polypectomy is therefore not a result of colonoscopy, but rather reflects the inherently low risk of patients free of endoscopically visible precancerous lesions,” wrote the study’s lead author, Dr. Hermann Brenner of the German Cancer Research Center in Heidelberg and his colleagues.
In the United States, guidelines for colorectal cancer screening with colonoscopy generally recommend screening every 10 years beginning at age 50. More vigilant screening, however, is typically recommended for those with a family history of colorectal polyps or cancer.
The study included nearly 3,600 participants. Case patients were 30 years of age or older who had been diagnosed with colorectal cancer based on symptoms or incidental findings from other procedures but not as a result of screening and were treated at 22 hospitals in southeastern Germany. Control subjects were selected from population registries. Information on previous colorectal endoscopies was obtained from interviews and medical record reviews.
Control subjects were nearly four times more likely than case patients to have had a previous negative colonoscopy. Overall, previous negative colonoscopy was associated with a 79 percent reduction in the risk of colorectal cancer. A single negative colonoscopy was associated with a 72 percent lower risk of developing colorectal cancer over the next 10 to 19 years, and a 60 percent lower risk at 20 years or longer. The lower risks were similar for men and women, former and never smokers, participants who had first-degree relatives previously diagnosed with colorectal cancer, and participants with a single previous colonoscopy.
All participants in the study were recruited between 2003 and 2007. Because colonoscopy was not routinely offered as a primary screening test for colorectal cancer in Germany until late 2002, many of the participants in the study who had undergone a colonoscopy did so because of positive findings from a fecal occult blood test that was prompted by symptoms or other indications, the authors explained.
This fact could limit the extent to which the results apply to a primary screening setting, the study authors noted. They suggested, however, that the long-term risk of colorectal cancer after a negative colonoscopy might be even lower in an unselected screening population. Indeed, although they note that the results should be confirmed in additional studies, the authors also point out that their study “supports suggestions that the majority of average-risk patients with a negative colonoscopy might not need another screening colonoscopy for at least 20 years, if at all.”
Further reading: “Sigmoidoscopy Markedly Reduces Colorectal Cancer Incidence, Mortality”
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