Individuals who underwent colonoscopies had a lower risk of colorectal cancer than those who did not get screened, according to a new study published in the New England Journal of Medicine. However, the reduction in risk was lower than expected, suggesting that a colonoscopy may not be "the magic bullet we thought it was"—though experts continued to emphasize that these screenings remain useful and that you "may reduce your risk of getting colorectal cancer by 20 to 30% if you get a colonoscopy."

Study details and key findings

For the study, researchers conducted a randomized trial involving 84,585 men and women between the ages of 55 and 64 from Poland, Norway, Sweden, and the Netherlands between 2009 and 2014. The trial, known as the Northern-European Initiative on Colorectal Cancer (NordICC), randomly assigned participants in a 1:2 ratio to either receive an invitation to undergo a single colonoscopy screening or receive the usual care.

In total, 28,220 participants were in the screening group, and 11,843 (42%) ultimately underwent a colonoscopy. The remainder of the participants were in the usual care group.

After a median follow-up of 10 years, 259 cases of colorectal cancer had been diagnosed in the invitation group compared to 622 cases in the usual care group. Through intention-to-screen analyses, the researchers found that the risk of colorectal cancer at 10 years was 0.98% in the invitation group and 1.20% in the usual care group—an overall reduction in risk of 18%.

The risk of death from colorectal cancer in the invitation group was 0.28%, compared to 0.31% in the usual care group. According to the researchers, this difference was not significant.

However, if all participants who were assigned to the invitation group had actually received a colonoscopy, the incidence of colorectal cancer would have been reduced by 31% and the risk of death by colorectal cancer by 50%.

Overall, the researchers found that 455 people would need to be invited to undergo a colonoscopy screening to prevent one case of colorectal cancer.

"Although we observed appreciable reductions in relative risks, the absolute risks of the risk of colorectal cancer and even more so of colorectal cancer-related death were lower than those in previous screening trials and lower than what we anticipated when the trial was planned," the researchers wrote.

Commentary

According to STAT, gastroenterologists have "reacted to the trial's results with a mixture of shock, disappointment, and even some mild disbelief."

Michael Bretthauer, a gastroenterologist who leads the clinical effectiveness group at the University of Oslo in Norway and the study's lead author, said he found the results disappointing, but that as a researcher, he had to follow the science.

"It's not the magic bullet we thought it was," Bretthauer said. "I think we may have oversold colonoscopy. If you look at what the gastroenterology societies say, and I'm one myself so these are my people, we talked about 70, 80, or even 90% reduction in colon cancer if everyone went for colonoscopy. That's not what these data show."

Samir Gupta, a gastroenterologist at the University of California, San Diego and the Veterans Health Administration, expressed similar sentiments. "This is a landmark study. It's the first randomized trial showing outcomes of exposing people to colonoscopy screening versus no colonoscopy. And I think we were all expecting colonoscopy to do better," he said. "Maybe colonoscopy isn't as good as we always thought it is."

However, several experts noted that while the study itself was robust, it also had several important limitations. For example, less than half of the people who were invited to get a colonoscopy in the study actually did so.

"I think it's just hard to know the value of a screening test when the majority of people in the screening didn't get it done," said William Dahut, chief scientific officer at the American Cancer Society, who was not involved in the study.

Gupta emphasized the findings do not mean that colonoscopies are not a useful screening tool. Instead, he said the findings suggest it may be time to reevaluate whether colonoscopies are the "gold standard" of colon cancer screenings.

"This study provides clear data that it's not as simple as saying, 'Colonoscopy is the most sensitive test, and therefore it is the best,'" he said. "It still prevented cancers."

According to Bretthauer, the true benefits of colonoscopies likely lie between the primary and secondary analyses of the study. "You may reduce your risk of getting colorectal cancer by 20 to 30% if you get a colonoscopy," he said, which brings its benefits in line with other common, but less invasive colorectal cancer tests.

Overall, Gupta said that even though the study returned smaller-than-expected benefits for colonoscopies, it still showed that the procedure reduced cancer incidence, which in turn reduced the patients' need for surgery, chemotherapy, and immunotherapies.

"The first message is that screening saves lives and prevents cancer. If we could have a chance to start everyone at age 45, I'd like that," Gupta said. "Second is you have many options. Someone who says, 'I'm way too busy, can't take 2 days off of work for a colonoscopy.' OK, we have stool-based options." (Chen, STAT, 10/9; Goodman, CNN, 10/10; Bassett, MedPage Today, 10/9; Bretthauer et al., New England Journal of Medicine, 10/9)