A single screening colonoscopy reduced colorectal cancer incidence by roughly 30% over 13 years — a meaningful improvement over earlier findings — but failed to produce a statistically significant reduction in colorectal cancer deaths, according to updated data from the largest randomized trial ever conducted on colonoscopy screening.
The new results from the NordICC trial were presented at Digestive Disease Week 2026 in Chicago May 2-6 and simultaneously published in The Lancet.
Researchers followed 84,583 adults aged 55 to 64 from Norway, Poland and Sweden who were randomly assigned either to receive an invitation for a one-time screening colonoscopy or to receive no screening.
Here are six takeaways from the study:
1. After 13 years, colorectal cancer developed in 1.46% of those in the screening group compared to 1.8% in the no-screening group — a risk ratio of 0.81 in intention-to-screen analyses, and 0.55 among those who actually completed the colonoscopy (per-protocol).
2. That incidence benefit has grown over time. At the trial’s 10-year follow-up, published in the New England Journal of Medicine in 2022, colonoscopy was associated with an 18% relative risk reduction in colorectal cancer.
3. The mortality picture, however, has not changed. Colorectal cancer deaths were 0.41% in the screening group and 0.47% in the no-screening group — a risk ratio of 0.88 that did not reach statistical significance.
“The first publication at 10 years showed an effect of around 20% risk reduction and no effect on mortality,” said principal investigator Michael Bretthauer, MD, PhD, a professor of medicine at the University of Oslo. “Some experts said 10 years was too short and expected the effect would be larger with longer follow-up. That is why we did a new analysis 3 years down the road.”
4. A key design issue complicates interpretation: the trial was built around an assumed baseline colorectal cancer mortality rate of 0.82% in the no-screening group. The observed rate came in at 0.47% — nearly half what was projected. That gap gutted the trial’s statistical power to detect a mortality benefit, since the original sample size calculations depended on a world where CRC deaths were far more common.
The trial was also limited by low screening uptake. Only about 42% of those invited to colonoscopy actually underwent the procedure — a real-world figure that, by design, dilutes the effect in intention-to-screen analyses.
5. Findings by sex raised additional questions. Aasma Shaukat, MD, of NYU Grossman School of Medicine, who wrote an editorial accompanying the paper, called the lack of CRC incidence reduction in women “quite concerning.”
“It implies women do not benefit from colonoscopy screening due to their low baseline risk of colorectal cancer,” Dr. Shaukat said. She noted that the absence of a significant proximal CRC benefit carries similar implications — that colonoscopy may not be reducing risk in the part of the colon it is hardest to reach and visualize.
6. The findings land in a context where colonoscopy’s reputation has largely been built on observational studies showing CRC mortality reductions ranging from 65% to as much as 88% — figures far exceeding what this randomized trial has produced. The growing incidence benefit — now at 30% and rising from 20% three years ago — represents real prevention. As one editorialist noted, the evidence supporting reductions in colorectal cancer incidence “is nevertheless a profound benefit on its own.”
The NordICC trial is designed for a 15-year primary analysis, meaning the most definitive mortality data are still to come.
At the Becker’s 32nd Annual Meeting: The Business and Operations of ASCs, taking place October 29-31 in Chicago, ASC leaders, surgeons and healthcare executives will explore strategies to drive growth, enhance operational performance, navigate reimbursement challenges and prepare for the future of ambulatory surgery. Apply for complimentary registration now.