Although colonoscopies have long been viewed as the "gold standard" for colorectal cancer screening, a recent study called that belief into question after its results found lower than expected benefits for the procedure. However, several health experts have highlighted limitations in the study and say that patients should not be discouraged from undergoing colonoscopies.

Experts push back on major colonoscopy study

According to a new study published in the New England Journal of Medicine, individuals who underwent colonoscopies had a lower risk of colorectal cancer than those who did not get screened, but the reduction in risk was lower than expected.

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.

Overall, 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.

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, and that getting a colonoscopy may not be "the magic bullet we thought it was."

However, several experts have since pushed back on the study, concerned that the findings may be interpreted in a way that discourages people from getting colon cancer screenings. According to MedPage Today, concerns about the study have largely focused on three areas:

1. The colonoscopy participation rate

Among the study's participants who were invited to undergo colonoscopies, only 42% actually received one. "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 (ACS).

Notably, the study found that 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 would have been reduced by 50%.

"[T]hat's message number one," said George Chang, from the University of Texas MD Anderson Cancer Center. "Colonoscopy is not effective if you don't do it, and so the effect was probably a lot smaller than expected because of the low compliance rate."

2. The colonoscopy operator quality

According to Bret Petersen, president of the American Society for Gastrointestinal Endoscopy, the quality of colonoscopies performed in the study may have varied due to different physician skillsets, endoscopy tools, and technology.

"Nearly 30% of the endoscopists who were included in the NordICC trial did not meet the adenoma detection rate (ADR) of 25% that is recommended in the U.S.—while the ADR average in the U.S. is above 40%," Petersen noted.

Because colonoscopy quality may have varied in the study, some experts are concerned that some endoscopists may have missed adenomas. "We expect a much higher percentage of an adenoma detection rate," said Raymond DuBois, director of the Hollings Cancer Center at the Medical University of South Carolina.

3. The length of follow up

Although the study had a median follow-up period of 10 years, Aasma Shaukat, from the NYU Grossman School of Medicine, said this was likely not long enough to accurately assess the mortality risks since colorectal cancer typically takes roughly 15 to 20 years to develop.

The study's authors "will do another analysis of the data in 5 more years, so it could be also that it was just too short of a duration, of observation, to see a significant impact," Shaukat said. "I would hate for people to jump off the screening bandwagon now because it might have been premature. The study needed more time to make these observations."

What does this mean for patients?

According to NPR, the study's findings are not likely to lead the United States to change its cancer screening recommendations. Currently, ACS recommends adults ages 45 and older be screened for colorectal cancer.

"Preventive cancer screenings are the best and most trusted way to save lives," said ACS CEO Karen Knudsen. "There's no reason to change that direction."

"We've all been trying to boost colorectal cancer screening, and what we don't want is to derail that effort or have our patients think that screening is not effective and forego it," Shaukat said. "We should mitigate any impression that this should deter, demotivate, or discourage people from undergoing colorectal cancer screening."

Shaukat also noted there are other tests patients can undergo to screen for colorectal cancer, such as image-based or stool-based tests, if they are not comfortable with getting a colonoscopy. "[A]t the end of the day, the best test is the one the patient is willing to complete," she said. (Bassett/Bankhead, MedPage Today, 10/12; Aubrey, "Shots," NPR, 10/13)