Efficacy of colonoscopy questioned in new study

Colonoscopy is a dreaded labor rite for many middle-aged adults.

The promise is that if you tolerate the awkwardness and invasiveness of a camera traveling the length of your large intestine every decade after age 45, you’ll have the best chance of detecting – and probably prevent – colorectal cancer. It is the second most common cause of cancer death in the United States. Approximately 15 million colonoscopy procedures are performed in the US each year.

Now, a landmark study suggests the benefits of colonoscopy for cancer screening may be overestimated.

The study marks the first time that colonoscopy has been directly compared with no cancer screening in a randomized trial. The study found only meager benefits for the group of people invited to the procedure: an 18 percent reduction in the risk of colorectal cancer and no significant reduction in the risk of dying from cancer. It was published Sunday in the New England Journal of Medicine.

Dr Michael Bretthauer, a gastroenterologist who leads the clinical efficacy team at the University of Oslo in Norway, said he found the results disappointing.

But as a researcher, he has to follow the science, “so I think we have to embrace it,” he said. “And we may have oversold the message in the last 10 years or so, and we had to narrow it down a bit.”

Other experts say that as good as this study is, it has important limitations and that these results don’t stop people from getting a colonoscopy.

Dr William Dahut, chief scientific officer at the American Cancer Society, said: “I think it’s hard to know the value of a screening test when the majority of people in the screening don’t do it. research.

Fewer than half of the people invited for a colonoscopy in the study – just 42% – actually did.

When the study authors restricted the results to people who actually received a colonoscopy — about 12,000 of the more than 28,000 invited to do so — the procedure was found to be more effective. It reduces the risk of colorectal cancer by 31% and the risk of dying from that cancer by 50%.

Bretthauer says the real benefit of a colonoscopy may lie somewhere in between. He said he thinks about the results of the full study – including those who did and did not receive colonoscopy after they were invited – because of the minimal amount of benefit that colonoscopy provides for a population. screened. He thinks the results from the small group of people who actually get the test is the maximum benefit people can expect from the process.

Then, based on his results, he hopes that a screening colonoscopy could reduce a person’s risk of colorectal cancer by 18% to 31% and their risk of death by 0%. up to 50%.

Still, he said, even 50% is “as low as I think people thought.”

Other studies have estimated greater benefits to colonoscopy, reporting that these procedures can reduce the risk of dying from colorectal cancer by up to 68%.


The NordICC study, which stands for the Nordic Initiative on Colon Cancer, included more than 84,000 men and women aged 55 to 64 from Poland, Norway and Sweden. No one had ever had a colonoscopy before. Participants were randomly invited to have a colonoscopy exam between June 2009 and June 2014, or they were followed up in the study without being screened.

In the 10 years after admission, the group invited to have a colonoscopy had an 18% lower risk of colorectal cancer than the unscreened group. Overall, the group invited to the screening also had a small reduction in their risk of dying from colorectal cancer, but that difference was not statistically significant – meaning it could simply be due to chance.

Prior to the NordiCC trial, the benefit of colonoscopy was measured by retrospective observational studies that compared the frequency with which colorectal cancer was diagnosed in those who received colonoscopy versus those who did not. examined.

However, these studies can be biased, so scientists looking at randomized trials blindly categorize people into two groups: those assigned to the intervention and those not. These studies will then follow both groups forward to see if there is a difference. These studies are difficult to do for colon cancer, which can be slow growing and can take years to be diagnosed.

The researchers said they would continue to follow the participants for another five years. It is possible that because colon cancers can grow slowly, more time will help refine their results and may show greater benefits to endoscopic screening.


Often, these kinds of disappointing results from such a large and robust study would be considered definitive enough to change medical practice.

But the study has some limitations that experts say need to be sorted out before doctors and patients give up colonoscopy to screen for cancer.

“I don’t think anyone should cancel their colonoscopy,” said Dr. Jason Dominitz, national director of gastroenterology at the Veterans Affairs Health Service.

“We know that colon cancer screening is effective,” he said in an interview with CNN. Dominitiz co-authored an editorial that ran alongside the study.

There are several options for colorectal cancer screening. These include a stool test to check for the presence of blood or cancer cells, and a test called a colonoscopy, which looks only at the lower part of the colon. Both have been shown to reduce cancer incidence and mortality from colorectal cancer.

“Other tests work through colonoscopy,” says Dominitz. “They identify people at high risk who would benefit from a colonoscopy, then a colonoscopy is done and the polyps are removed, such as preventing the person from getting colon cancer in the first place or identify colon cancer at a treatable stage.”

Polyps are benign tumors that can turn cancerous. They are often removed when identified during a screening colonoscopy, which can reduce a person’s risk of colorectal cancer in the future.

Studies are underway in Spain and the United States testing colonoscopy head-to-head with stool testing to see which is most effective.


Dominitz said the randomized controlled trial is a trial of advice as well as a trial of the value of colonoscopy.

“If you asked the population to do something, how much impact would it have?” he say.

Overall, the study found that simply inviting people for a colonoscopy didn’t have a major beneficial effect in these countries, in part because so many people didn’t.

Dominitz suggested that low participation could be partly explained by the context of the study. Colonoscopy is not as common in the participating countries as it is in the United States. In Norway, official colorectal cancer screening recommendations were not made until last year, he said.

“They don’t see the public service announcements. They don’t hear Katie Couric talk about colon cancer screening. They don’t see the billboards in the airport and nothing,” he said. “So I think an invite shown in Europe might be slightly different from an invite shown in the US.”

In the US, according to data from the US Centers for Disease Control and Prevention, about one-fifth of adults between the ages of 50 and 75 have never been screened for colorectal cancer.

If you’re nervous about going for a colonoscopy, the US Preventive Services Task Force recommends a variety of methods and protocols that can help detect colorectal cancer. It recommends screening with tests that check for blood and/or cancer cells in the stool every one to three years, CT colonoscopy every 5 years, flexible colonoscopy every 5 years, colonoscopy flexible colonoscopy every 10 years in combination with a stool test for annual blood tests or a colonoscopy every 10 years.

In 2021, the task force lowered the recommended age to begin routine colorectal cancer screening from 50 to 45 because the cancer is becoming more common in young people.

When it comes to colorectal cancer, he says, the tests can only be effective if people are willing to have them.

As proof, he points to preliminary results from a large randomized trial from Sweden, which was a colonoscopy trial, a FIT trial, and no screening at all.

Results collected from more than 278,000 enrollees between March 2014 and the end of 2020 showed that 35% of the group assigned to colonoscopy actually had one, compared with 55% assigned to the stool test group.

So far, slightly more cancers have been detected in the group assigned to stool testing than in the group assigned to endoscopy – “so getting screened is really key!” Dominitz said.


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