Colonoscopies detect and remove growths called polyps in the large bowel. We are often told that this screening procedure reduces the likelihood of colorectal cancer because the polyps that could become cancerous are removed.
Once people have had a polyp removed, they are supposed to return for periodic colonoscopies, and they frequently are found to have additional polyps. A Norwegian study published in The New England Journal of Medicine found that people who had low-risk polyps removed during a colonoscopy had a 25% lower risk of death from colorectal cancer during the next seven years than the general population.
If the polyps were classified as high-risk, however, the colonoscopies didn’t reduce the risk of dying from colorectal cancer; in fact these people had a 16% higher likelihood of dying from colorectal cancer during the study period than the general population. The authors proposed several possible explanations: removal of the polyp during the colonoscopy might have been incomplete; the colonoscopy might not have found all of the polyps; or people whose bodies create high-risk polyps will probably continue to develop them, perhaps in a time frame shorter than the follow-up for this study. Although colonoscopies should still be perceived as valuable, they may not be quite as protective as expected.
[New England Journal of Medicine, Aug. 28, 2014]
From The People’s Pharmacy perspective, this underscores the danger of complacency in relying too heavily on a screening test to “protect” us from cancer. The colonoscopy screening provides valuable information; if a person is found to have a high-risk polyp, he or she should pay close attention to possible symptoms such as a change in bowel habits and act promptly to have them evaluated. They may also benefit from a personalized recommendation to have repeat colonoscopy more frequently than those without high-risk polyps.
You can learn more about preventing and detecting colorectal cancer from this hour-long interview with Dr. Mark Pochapin.
