Colonoscopy is one of the screening exams for colorectal cancer, one of the most common cancers. And yet, a randomized study published recently concludes that it does not reduce the risk of mortality linked to this cancer. Explanations.
Article updated on October 11, 2022
Going through a colonoscopy is an unpleasant and dreaded moment for patients. The intervention consists in exploring with a camera the rectumrectumI’small intestinesmall intestine and the large intestine looking for polyps that could turn cancerous in years to come; 60 to 80% of colon cancercolon cancer follow the detection of a massmass abnormal in the intestine. It is an integral part of the strategy of screeningscreening colorectal cancer, one of the most common among men and women over 50, and is recommended by the High Authority for Health.
Until today, none randomized studyrandomized study did not conclude that colonoscopy was effective in reducing mortality due to colorectal cancercolorectal cancer, and by extension, that this screening test is safe for health and does not increase the risk of death from any cause. A study published in The NEJM, the NordICC trial, conducted in Norway, Poland and Sweden, tackled this problem head-on. The conclusions go against what was supposed: this test does not reduce the risk of mortality due to colon cancer. This does not mean that you should do without colonoscopy to detect colon cancer. As indicated by the results presented below, it is an effective examination for locating polyps or adenomas precancerousprecancerous attached to the colon.
Colonoscopy and incidence of colorectal cancer
the protocolprotocol of the study replicates a colorectal cancer screening program. Among the 80,000 participants in the three countries, some are invited to undergo a colonoscopy (28,000 people), of which 42% will actually pass the examination. The incidence of colon cancer and the deaths it causes are followed over 10 years and compared to 56,000 people who did not receive an invitation and did not have a colonoscopy. The scientists made sure that the latter did not pass one outside theclinical testclinical test.
At the beginning of the ten years of follow-up, the scientists first observed an increased risk of colorectal cancer in patients asked to be screened – an expected trend since screening reveals the presence of cancer. But after six years of follow-up, the risk of colorectal cancer in people who are not screened becomes greater. In total, the risk of colorectal cancer is 0.98 in screened patients and 1.20 in unscreened people, i.e. a reduction in risk of 18%. Colonoscopy can reduce the risk of developing colorectal cancer. Of the 42% of guests who actually took the exam, adenomasadenomas precancerous were detected and removed in 30% of them, thus preventing the possible formation of a tumortumor later.
No benefit on mortality
The same follow-up was done for the risk of death from colorectal cancer or any other cause. In this case, there is no benefit for the screened patients. After ten years of follow-up, the risk of death linked to colon cancer is 0.28% (72 deaths recorded) for people screened by colonoscopy and 0.31% for people not screened. In the screened group, the scientists listed 11.03% of deaths from all causes in the “screened” group and 11.04% in the “unscreened” group. The study therefore shows that colonoscopy has no benefit on mortality due to colorectal cancer.
The study suffers from several weaknesses related to its method. In an analysis per-protocol, in which it is considered that all people eligible for a colonoscopy actually do it (which is not the case in reality), scientists observe a 30% reduction in the risk of colorectal cancer and related deaths. 50% ci. A benefit that the authors consider underestimated because the calculations could not be adjusted for all the variables due to the large size of the workforce and the differences between the Norwegian, Polish and Swedish populations which constitute the cohortcohort. analysis per-protocol also concludes that the calculated benefit of colonoscopy is greater in Norway than in Poland; the absolute risk of colon cancer being itself higher in Norway than in Poland.
THEAmerican Society for Gastrointestinal Endoscopy (ASGE) issued a press release following the NordICC trial which stipulated that : “The “per protocol” analysis, which considers people who have had a colonoscopy, there is a 50% reduction in mortality. This is consistent with overwhelming evidence from case and cohort studies that colonoscopy prevents colorectal cancer and associated deaths. This new study has too many unexplained problems to change the consensus about the benefit of colonoscopy. Colonoscopy, with modern endoscopes and trained endoscopists, continues to be the most proven and effective way to detect and prevent colorectal cancer. »
Colonoscopy or no colonoscopy?
Colonoscopy is not the only possible screening test to prevent colorectal cancer, there is in particular the sigmoidoscopysigmoidoscopy. This test less invasiveinvasive allows you to observe only the rectum, the sigmoid colon and the left colon, unlike colonoscopy which goes further up the digestive system. Sigmoidoscopy requires fewer medical resources to perform, but it has gradually been replaced by colonoscopy. Yet scientists note, about the results per-protocol presented before, that: ” These results suggest that colonoscopy screening may not be much more effective in reducing the risk of colorectal cancer than sigmoidoscopy. Despite everything, colonoscopy remains the reference technique. In France, screening for colon cancer (a stool analysis and a colonoscopy in the event of an abnormality) is recommended for all people aged 50 to 74 and reimbursed by health insurance.
The message to keep in mind is that colonoscopy remains an effective way to prevent colon cancer and that if your doctor recommends it, there is no reason not to go for it. If this test requires fairly substantial medical care, most of the time anesthesia and rigorous preparation to clean the intestines, and is not free of risk (that of hemorrhage or perforation of the intestine being the most serious, but the least frequent), it makes it possible to identify a precancerous mass before it is too late. This does not prevent scientists from carrying out independent scientific studies to estimate the real benefit of this practice. the NordICC trial alone is not enough to change the recommendations, but it may have raised a legitimate question.