CNN
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For many middle-aged adults, colonoscopy is a terrifying coming-of-age ritual. The promise is that if you endure the embarrassment and invasiveness of having the camera travel the length of your large intestine once every ten years after age 45, you have the best chance of contracting—and perhaps preventing—colorectal cancer. It is the second most common cause of cancer death in the United States. Approximately 15 million colonoscopies are performed in the United States each year.
Now, a landmark study suggests that the benefits of colonoscopy for cancer screening may be overestimated.
The study marks the first time that colonoscopy has been directly compared with cancer-free screening in a randomized trial. The study found little benefit for those invited to undergo the procedure: an 18 percent lower risk of developing colorectal cancer and no significant reduction in the risk of dying from cancer. It was published Sunday in the New England Journal of Medicine.
Study investigator Dr. Michael Bretthauer, a gastroenterologist who led the clinical effectiveness 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 accept it,” he said. “And we’ve probably oversold that information over the last 10 years or so, and we have to go back a little bit.”
Other experts say that while the study is good, it has major limitations and the results shouldn’t stop people from getting colonoscopies.
“I think it’s hard to know the value of a screening test when the majority of people in screening don’t complete the screening test,” said Dr. William Dahout, chief scientific officer of the American Cancer Society, was not involved in the study.
In the study, less than half of those invited for a colonoscopy — just 42 percent — actually got one.
When the study authors limited the results to people who actually had colonoscopies — about 12,000 of the more than 28,000 people invited — they found the procedure to be more effective. It reduced the risk of developing colorectal cancer by 31% and the risk of dying from the cancer by 50%.
Bretthauer said the real benefit of colonoscopy may lie somewhere in the middle. He said he sees the results of the full study — including those who did and did not undergo colonoscopy after being invited — as the minimal benefit that colonoscopy provides for the screening population. He believes that the results of the part of people who are actually tested are the greatest benefit people can get from the program.
So, based on his results, he predicts that colonoscopy may reduce a person’s chance of developing colorectal cancer by 18% to 31%, and reduce their risk of death from 0% to as much as 50%.
But, even at 50 percent, “I think everyone thinks it’s on the low end,” he said.
Other studies have estimated greater benefits from colonoscopy, reporting that these procedures can reduce the risk of dying from colorectal cancer by as much as 68 percent.
The NordICC study, representing the Nordic Colon Cancer Initiative, 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 undergo colonoscopy between June 2009 and June 2014, or they were followed without screening.
Within 10 years of enrollment, the group invited for colonoscopy had an 18 percent lower risk of developing colorectal cancer than the unscreened group. Overall, those invited to the screening also had a slightly lower risk of dying from colorectal cancer, but the difference was not statistically significant—meaning it may have been a result of chance.
Before the NordiCC trial, the benefits of colonoscopy were measured through observational studies that looked back and compared the frequency of colorectal cancer diagnoses in people who had colonoscopy and those who did not.
However, these studies can be biased, so scientists seek randomized trials that blindly divide people into two groups: those assigned to the intervention, and those who did not. The studies then follow the two groups in time to see if there is a difference. For colon cancer, these studies are difficult because colon cancer grows slowly and can take years to be diagnosed.
The researchers said they will continue to follow the participants for five years. Possibly because colon cancer grows slowly, more time will help improve outcomes and may show greater benefit from colonoscopy.
Often, those disappointing results from such a large, powerful study would be considered enough to change medical practice.
But the study has some limitations that experts say need to be addressed before doctors and patients abandon colonoscopy for cancer screening.
“I don’t think anyone should cancel their colonoscopy,” said Dr. Jason Dominitz is the National Director of Gastroenterology at the Veterans Health Administration.
“We know colon cancer screening works,” he told CNN. Dominitiz co-authored an editorial that ran concurrently with 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 sigmoidoscopy, which examines only the lower part of the colon. Both have been shown to reduce cancer rates and colorectal cancer deaths.
“Those other tests work through colonoscopy,” Dominitz said. “They identify high-risk groups that could benefit from colonoscopy, then having a colonoscopy and removing polyps, for example, could prevent an individual from developing colon cancer in the first place, or it could identify colon cancer in a treatable stage. ”
Polyps are benign growths that can turn into cancer. They are usually removed when they are identified during a colonoscopy, which can reduce a person’s risk of developing colorectal cancer in the future.
Studies are underway in Spain and the United States to test colonoscopy head-to-head with stool examination to see which method is most effective.
Dominitz said the randomized controlled trial was both a test of recommendations and a test of the value of colonoscopy.
“If you ask people to do something, how big of an impact will it have?” he said.
Overall, the study found, simply inviting people to have colonoscopies did not have a large beneficial effect in these countries, in part because many did not.
Dominitz believes that low participation can be partly explained by the research environment. Colonoscopy is not as common in the countries participating in the study as it is in the United States. In Norway, he said, official colorectal cancer screening recommendations were not introduced until last year.
“They don’t see public service announcements. They don’t hear Katie Couric talking about getting screened for colon cancer. They don’t see billboards in airports or anything,” he said. “So I think the invitation to show in Europe may be different than the invitation to show in the United States.”
In the U.S., according to the U.S. Centers for Disease Control and Prevention, about one in five adults between the ages of 50 and 75 has never been screened for colorectal cancer.
If you’re nervous about having a colonoscopy, the U.S. Preventive Services Task Force says there are various methods and protocols available to detect colorectal cancer. It recommends checking stool for blood and/or cancer cells every 1 to 3 years, colon CT scan every 5 years, flexible sigmoidoscopy every 5 years, and flexible sigmoidoscopy every 10 years in combination with stool Check up blood every year, or colonoscopy every 10 years.
In 2021, the task force lowered the recommended age to start routine screening for colorectal cancer from 50 to 45, as cancer becomes more common in younger people.
When it comes to colorectal cancer, it only works if people are willing to get tested, he said.
As evidence, he points to early results from a large randomized trial in Sweden that is testing colonoscopy, FIT testing and no screening at all.
Results collected from more than 278,000 people enrolled between March 2014 and the end of 2020 found that 35 percent of those assigned to a colonoscopy actually got one, compared with 35 percent of those assigned to a stool exam. 55%.
So far, slightly more cancers have been detected in the group assigned to stool testing than in the group assigned to colonoscopy — “so participation in screening is really key!” Dominic said.