Colonoscopy Screening May Not Be as Effective as Previously Thought, But Still Saves Lives

It remains the most helpful tool we have for preventing and diagnosing colon cancer.

A doctor and a patient sit at a desk for a medical consultation.

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Fast Facts

  • A new, widely-covered study called into question the real-world benefits of colonoscopy screening for colorectal cancer.
  • Though colonoscopy was still found to be beneficial in preventing and reducing deaths from the disease, it was not as helpful as previously thought.
  • Healthcare providers maintain that colonoscopy is still a key tool in preventing and diagnosing colon cancer, and that the findings should not deter anyone from getting screened.

Though the benefits of colonoscopies have come into question recently, gastroenterologists maintain that they are still the best tool we have, not only to detect and prevent colorectal cancer, but to diagnose other intestinal diseases as well.

The highly publicized study, published October 9 in the New England Journal of Medicine, found that colonoscopy screenings cut the risk of colon cancer by about a fifth—a far lower risk reduction than previous research had found. Colonoscopies had little effect on reducing the risk of death from colon cancer, as well. 

The findings, labeled as “surprising and disappointing” in an accompanying editorial, seemed to call into question whether the routine screenings are quite as useful—or as necessary—as previously thought.

Healthcare providers and professionals say they are—and that the study shouldn’t deter people from getting colonoscopies in the future.

“Colonoscopy is the gold standard. It is a very valuable tool for detecting numerous gastrointestinal diseases,” Sameer Berry, MD, MBA, a gastroenterologist at New York Gastroenterology Associates and Chief Medical Officer at Oshi Health, told Health . “It is one of the only tools that allow us to directly view and biopsy the digestive tract without making any incisions and with very minimal risk.”

Here, gastroenterologists help to explain the new research—including how it could have been misinterpreted in the media—and why routine colonoscopy screening is still largely beneficial.

Colonoscopies Are Only Effective When People Get Them

Colonoscopies are used as both a screening and diagnostic tool. The procedure allows a healthcare provider to look inside the rectum and colon, to see if there’s any potentially harmful changes (swelling, ulcers, polyps, cancer).

Historically, colonoscopies have shown to be highly effective in preventing colon cancer (a 40%–69% decrease in disease incidence) and death from the disease (a 29%–88% decrease in colon cancer-related deaths). But those statistics largely came from cohort studies, which, though useful, may overestimate the procedure’s real-world effectiveness.

To get a closer look at the true effectiveness of colonoscopies on colon cancer prevention and disease-related death, researchers conducted a randomized trial—the Nordic-European Initiative on Colorectal Cancer (NordICC)—involving nearly 85,000 “presumptively healthy” men and women between the ages of 55 and 64.

The participants—from Poland, Norway, and Sweden—either received an invitation to get a colonoscopy (“the invited group”) or did not get an invite or a screening (“the usual-care group”). 

Looking at the entire group over a period of 10 years, colonoscopy screening lowered the risk of cancer by 18% (the invited group had a 0.98% risk, compared to the 1.2% risk of the usual-care group). Reduction in the risk of death, however, was not significant. Overall, researchers determined that 488 people would have to be invited for a colonoscopy screening to prevent one case of colon cancer within a 10-year period.

However, when researchers looked at only those who underwent a colonoscopy after receiving an invite—just 11,843 participants out of more than 28,000, or 42%— the risk reductions improved. 

In that adjusted analysis, colonoscopies were estimated to reduce the incidence of cancer by 31%, and the risk of colon cancer-related death by 50%—numbers closer to previous study findings, and potentially more realistic.

“The estimates that people, at least in the US, were citing—80%–90%—were just too high and they were not supported by evidence. I think it was too optimistic,” lead study author Michael Bretthauer, MD, PhD, professor of medicine at the University of Oslo and gastroenterologist at Oslo University Hospital, told Health. “The real effect is what the trial shows, so 50% or lower, which is still interesting for many people but it’s not what people thought it would be.”

Differences in Colonoscopy Screening in the US and Europe

The study looked at a group of European participants—but experts say that the rising rates of colorectal cancer in the US, primarily among younger populations, may mean that colonoscopy could provide greater benefit in America.

“US youths are experiencing colorectal cancer rates much higher than their European counterparts,” said Dr. Berry, citing a 2019 letter published in the journal Gut. “Since [those] rates are higher in the US, screening protocols are more likely to be beneficial.”

There’s also the fact that colonoscopy screening just isn’t as common in the European countries where the participants were from, especially not in 2009, when the study began.

According to study authors, Poland had an opportunistic screening program—in which screening only happens if a person or their healthcare provider requests it—in only some areas. In other countries, there was no organized screening process. It wasn’t until the last four years of the trial that colorectal cancer screenings were gradually introduced in participating countries.

Meanwhile, in the US, all adults are recommended to get colonoscopies to screen for colon cancer beginning at age 45, unless they have certain risk factors that increase their chances of developing colon cancer—then screenings may begin earlier. That’s a new recommendation as of May 2021. Previously, in 2016, the US Preventive Services Task Force recommended colorectal cancer screening begin at age 50.

Additional Study Limitations

Though the current study provides information from a 10-year follow-up with participants, the trial is still technically ongoing, with plans to follow up with participants again in another five years—a point at which more appreciable benefits may be seen.

“The study will likely demonstrate greater benefit after the anticipated 15 years of follow-up,” Bret Petersen, MD, president of the American Society for Gastrointestinal Endoscopy and professor of medicine in the division of gastroenterology and hepatology at the Mayo Clinic, told Health.

According to Dr. Petersen, the timeline for the development of cancer—and the benefit of clearing precancerous polyps—likely extends to 15 years or more.

Colonoscopies are also extremely dependent on the healthcare providers that perform them, according to the new study’s accompanying editorial. Those professionals—called endoscopists—have what’s called an adenoma detection rate (ADR), or the frequency at which they detect and remove precancerous polyps.

Endoscopists with a higher ADR provide their patients with greater protection. The recommended minimum ADR is 25%, according to a review published in 2015; and 29% of endoscopists in the current study had an ADR below that. However, that could be due to a lower presence of polyps in some populations overall, Dr. Bretthauer told NPR. He also said that the ADRs in both Poland and Sweden were “well above the current threshold for good quality.”

Making the Decision to Get a Colonoscopy

Colonoscopy remains the most sensitive and beneficial screening tool we have for both the prevention and detection of colorectal cancers. Though the most recent study may not have lived up to previous findings, it has not—and likely will not—change the current screening recommendations in the US.

“Nothing has changed about our understanding of the effectiveness of colonoscopy screening in 2022 in North America,” said Dr. Petersen. “Even in the United States the performance and quality of exams have increased greatly since the era of this study in 2009-2014.”

It’s important to note too that colonoscopy is not only a colorectal cancer screening tool—the procedure is also an essential diagnostic tool for other diseases, like inflammatory bowel disease (IBD) and to further investigate various gastrointestinal symptoms.

The study also indirectly highlights the importance of taking control of your health, and choosing to do the recommended screenings for better health outcomes.

“I want people to take away that it requires more responsibility for your own health and your life,” said Dr. Bretthauer. “Why would you be less independent in your decision-making with regard to health?” 

This also means being aware of your own personal risk for colorectal cancer. The best way to determine that is by meeting with a healthcare provider, like a primary care doctor or gastroenterologist. 

If you cannot or are unwilling to undergo a colonoscopy, there are other options, such as sigmoidoscopy and stool testing—but just know that most other procedures, if something comes back as abnormal, will need to be verified through a colonoscopy.

“The conclusion that Americans and their doctors should take is that people are reluctant to get colonoscopies,” said Dr. Berry. “When people don’t get a colonoscopy, they don’t reap the benefits of early cancer detection. If you catch colorectal cancer early, it’s treatable; but if you don’t detect it early, it’s [likely] not.”

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