Colonoscopy Trial Shows Clear Cancer Prevention but Mixed Results on Saving Lives

Updated results from a long-term European study confirm that colonoscopy screening can lower the risk of developing colorectal cancer, but the procedure’s ability to reduce deaths from the disease remains less certain.

After tracking participants for 13 years, researchers found that 1.46% of people who had a colonoscopy developed colorectal cancer, compared with 1.80% of those who did not get screened. This translates to a 19% lower risk of getting the disease when looking at all invited participants, and a 45% lower risk among those who actually underwent the procedure. These findings come from the NordICC trial, led by Dr. Michael Bretthauer of the University of Oslo, Norway, and his team.

However, when it came to deaths from colorectal cancer, the numbers were not statistically different. Among the screening group, 0.41% died from the disease, compared with 0.47% in the no-screening group. The risk reductions—12% in the broader analysis and 30% among those who got screened—were not strong enough to rule out chance.

The results were presented at the Digestive Disease Week meeting and published simultaneously in The Lancet.

These findings mirror what the study showed at the 10-year mark. At that point, 0.98% of the screening group had developed colorectal cancer versus 1.20% in the no-screening group, while death rates were 0.28% and 0.31%, respectively.

Bretthauer noted that a common criticism of the earlier results was that 10 years might be too short to see a clear effect on mortality. But the updated data suggest otherwise.

“Lesson learned number one with this paper is that it doesn’t get better with longer follow-up time,” Bretthauer said.

He also pointed out that the death rate in the no-screening group (0.47%) was much lower than what researchers had expected when the trial was designed (0.82%). This is likely because treatments for colorectal cancer have improved dramatically.

“We know from cancer statistics that survival rates for patients with colorectal cancer have become a lot higher than they were 10, or even 5, years ago,” Bretthauer explained. “So, a lot more people who get the disease survive because we have much better oncological treatments—better surgical treatment, better radiation treatment, and immunotherapy in the last 4 or 5 years. That’s all good news for patients.”

He added that while the death rate in the no-screening group is not zero, “it’s approaching zero, and it’s hard to be better than that.”

In a commentary published alongside the study, Dr. Aasma Shaukat of NYU Grossman School of Medicine wrote that the longer-term results “compel a recalibration of what colonoscopy can—and cannot—achieve at the population level.”

She noted that better treatments change the equation for screening benefits. “This evolving therapeutic landscape fundamentally changes the arithmetic of screening benefit. Colonoscopy clearly prevents some cancers, but when prognosis for clinically detected colorectal cancer improves, the incremental mortality benefit that screening can deliver inevitably shrinks.”

Shaukat added that even if longer follow-up eventually shows a statistically significant reduction in deaths, “the absolute effect is likely to remain small.” She raised a key question for doctors and policymakers: “How many procedures, with what opportunity costs, are required to avert one death in contemporary practice?”

Her bottom line: “Colonoscopy prevents some cancers, but in an era of improving colorectal cancer care, the scale and nature of its benefits are more modest—and more nuanced—than many had long assumed.”

The NordICC trial included 84,583 people from Norway, Poland, and Sweden. Of these, 28,217 were randomly assigned to the screening group, and 56,366 to the no-screening group. Only 42% of those invited for screening actually showed up for the procedure.

Bretthauer highlighted two other important findings from the updated analysis. First, colonoscopy appears to work better in men than in women. Among men, 1.69% of those screened developed cancer versus 2.19% in the no-screening group—a 23% lower risk. Among women, the rates were 1.24% and 1.43%, respectively—a 13% lower risk that was not statistically significant.

Second, colonoscopy was more effective at detecting and preventing cancers in the lower part of the colon (distal) compared with the upper part (proximal). The risk of distal cancer was 0.87% in the screening group versus 1.11% in the no-screening group—a 21% reduction. For proximal cancer, the rates were 0.51% and 0.56%, a smaller 9% difference that was not statistically significant.

Shaukat noted that the trial has limitations, including the low participation rate of 42%. But its strengths—random assignment, screening-naive populations, minimal contamination, and complete long-term registry data—make it uniquely valuable.

So how should these results guide real-world decisions? Bretthauer said that when he explains the numbers to patients, most understand them quickly. “People will decide very differently, with the same information and the same numbers. At least they’re informed in the way they understand, and then it’s up to [them] to decide.”

For policymakers, Shaukat emphasized that colonoscopy is an effective cancer-prevention tool, especially when people actually get it done. But she also urged a broader view: “Modest or uncertain mortality benefits, combined with low background colorectal cancer mortality, demand explicit consideration of value. In many settings, investments in tobacco control, obesity prevention, or optimizing treatment pathways could yield larger gains in population health per unit of expenditure.”

Source: MedPage Today