New study questions the effectiveness of colonoscopies in cancer screening

Colonoscopies are a dreaded rite of passage for many middle-aged adults. The promise is that if you can put up with the embarrassment and invasiveness of having a camera run the length of your large intestine once every decade after age 45, you’ll have the best chance of detecting — and perhaps preventing — colorectal cancer.

In Brazil, approximately 40,000 new cases are detected each year and about 20,000 deaths from the disease are recorded. It is the second most common cause of cancer death in the United States, with about 15 million colonoscopies performed in the US each year.

Now, a landmark study suggests that benefits of colonoscopies for cancer screening may be overestimated .

The study marks the first time colonoscopies have been directly compared with no cancer screening in a randomized trial. The study found only meager benefits for the group of people invited to have the procedure: an 18% lower risk of getting colorectal cancer and no significant reduction in the risk of dying from cancer. The findings were published Sunday in The New England Journal of Medicine.

Study researcher Michael Bretthauer, a gastroenterologist who leads the clinical efficacy group 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 over-sold the message in the last 10 years or so, and we have to back off a little bit.”

Other experts say that as good as this study was, it has important limitations, and these results shouldn’t deter people from having colonoscopies.

“I think it’s hard to know the value of a screening test when most people in the screening haven’t done it,” said William Dahut, scientific director of the American Cancer Society, who was not involved in the study.

Less than half of the people invited to have a colonoscopy in the study – just 42% – actually had one.

When the study authors narrowed the results down to people who actually had colonoscopies — about 12,000 of the more than 28,000 who were asked to do so — the procedure proved more effective. It reduced the risk of colorectal cancer by 31% and cut the risk of dying from that cancer by 50%.

Bretthauer stated that the true benefits of colonoscopy likely lie somewhere in the middle. He said he thinks of the results of the full study — including people who did and didn’t have colonoscopies after being invited — as the minimal amount of benefit colonoscopies provide to a screened population. He thinks of the results of the subset of people who actually had the test as the maximum benefit people could expect from the procedure.

Based on his results, he expects that screening colonoscopy is likely to reduce a person’s chances of colorectal cancer by 18% to 31%, and their risk of death by 0% to 50%.

But, he said, up to 50% is “at the lower end of what I think everybody thought it would be.”

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

First randomized colonoscopy trial

The NordICC study, which stands for Northern Europe Colon Cancer Initiative, included more than 84,000 men and women aged 55 to 64 from Poland, Norway and Sweden. None had had a colonoscopy before. Participants were randomly invited to have a screening colonoscopy between June 2009 and June 2014, or were followed into the study without being screened.

In the 10 years after enrollment, the group invited to have colonoscopies had a 18% lower risk of colorectal cancer than the group that was not tracked. Overall, the group invited to the screening also had a small reduction in risk of death from colorectal cancer but this difference was not statistically significant – meaning it could simply be due to chance.

Prior to the NordiCC study, the benefits of colonoscopies were measured by observational studies that looked back in time to compare how often colorectal cancer is diagnosed in people who received colonoscopies. versus those who did not receive.

These studies may be subject to bias, however, scientists look for randomized trials that blindly classify people into two groups : those who are designated to receive an intervention and those who are not. These studies follow the two groups over time to see if there are differences. These studies have been difficult to do for colon cancer, which can grow slowly and it can take years to be diagnosed.

The researchers say they will continue to follow the participants for another five years. It could be that since colon cancers can grow slowly, more time will help refine your results and may show greater benefits for colonoscopy screening.

Results need careful interpretation

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

But this study has some limitations that experts say need to be addressed before doctors and patients give up on colonoscopies for cancer screening.

“I Think no one should cancel their colonoscopy “, said Jason Dominitz, national director of gastroenterology at the Veterans Health Administration.

“We know colon cancer screening works,” said Dominitiz, who also co-authored an editorial accompanying the study.

There’s a lot cancer screening options colorectal. This includes stool tests that check for blood or cancer cells and a test called a sigmoidoscopy, which looks only at the lower part of the colon. Both have been shown to reduce cancer incidence and colorectal cancer deaths.

“These other tests work through colonoscopy,” Dominitz said. “They identify high-risk people who would benefit from colonoscopy, then colonoscopy is done and removes polyps, for example, that prevent the individual from getting colon cancer in the first place, or identifies colon cancer at a treatable stage.”

You polyps are benign tumors that can turn into cancer. They are usually removed when identified during a screening colonoscopy, which can lower a person’s risk of colorectal cancer in the future.

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

Best way to screen for colorectal cancer

Dominitz said this randomized controlled trial was as much a test of counseling as a test of the value of colonoscopy.

“If you ask the population to do something, what impact will it have?” he said.

Overall, the study found that just inviting people to have a colonoscopy did not have much of a beneficial impact in these countries, in part because many people did not.

Dominitz thinks the low turnout can be partially explained by the study setting. Colonoscopies are not as common in the countries involved in the study as they are in the United States. In Norway, he said, official colorectal cancer screening recommendations did not arrive until last year.

“They don’t see the public service announcements. They don’t hear Katie Couric talking about getting tested for colon cancer. They don’t see the billboards at the airport and other incentives,” he said. “So an invitation to be shown in Europe is, I think, probably a little different than an invitation to be shown in the US.”

In the US, according to data from the US Centers for Disease Control and Prevention (CDC), about 1 in 5 adults between the ages of 50 and 75 has never been screened for colorectal cancer.

If you’re embarrassed about having a colonoscopy, the US Preventive Services Task Force says a variety of methods and regimens work to detect colorectal cancer. Recommends screening with tests that check for blood and/or cancer cells in the stool every one to three years, a CT scan of the colon every five years, a flexible sigmoidoscopy every five years, a flexible sigmoidoscopy every 10 years combined with tests of stool to check for blood annually or a colonoscopy every 10 years.

In 2021, the task force lowered the recommended age to start routine colorectal cancer screening from 50 to 45 years, because cancer is becoming more common in younger adults.

When it comes to colorectal cancer, Dominitz said, tests can only be effective if people are willing to have them.

As evidence, he points to the first results of a large randomized trial from Sweden that is testing colonoscopy, FIT testing, and no screening.

Results collected from more than 278,000 people enrolled between March 2014 and the end of 2020 indicated that 35% of the group assigned to have a colonoscopy actually had one, compared to 55% who were assigned to the stool test group.

To date, slightly more cancers have been detected in the group assigned to the stool test than in the group assigned to have a colonoscopy – “so participation in screening is really critical!” said Dominitz.