Multinational randomized trial of long-term effects of colonoscopy screening on colorectal cancer incidence and mortality

In a population-based randomized trial, 84 583 men and women aged 55-64 years at enrollment from Norway, Poland, and Sweden were randomized 1:2 to colonoscopy screening or no screening. The primary outcomes were colorectal cancer (CRC) incidence and mortality after 10-15 years of follow-up in intention-to-screen analyses. At 13 years of follow-up, CRC incidence was 1.46% in the screening group versus 1.80% in the no-screening group, with risk ratio (RR) 0.81 (95% CI 0.71-0.90) in intention-to-screen analysis and 0.55 (0.33-0.81) in per-protocol analysis. The risk for proximal CRC was not significantly different between the groups; the risk for distal CRC was 0.87 in the screening group and 1.11% in the no-screening group (RR 0.79; 95% CI 0.65-0.89). CRC mortality was 0.41% in the screening group and 0.47% in the no-screening group (intention-to-screen RR 0.88; 95% CI 0.68-1.08; per-protocol 0.70; 0.26-1.25). The observed CRC mortality in the non-screening group was substantially lower that expected at the time of designing the trial (0.82%). The authors conclude that one colonoscopy significantly reduced CRC incidence but not mortality over 13 years.