NordICC Trial Results in Line with Expected Colorectal Cancer Mortality Reduction After Colonoscopy

Colonoscopy screening is a widely recommended method for detecting colorectal cancer (CRC) in countries across the world. However, until recently, no randomized controlled trials (RCT) demonstrated its effectiveness in average-risk individuals. Recently, Bretthauer et al. published preliminary results of a multicentre RCT, the NordICC trial, that investigated the effects of once-only colonoscopy screening on CRC incidence and mortality. In the intention-to-screen analysis, which compared participants not offered screening to those offered screening regardless of participation, they found that the invited group had an incidence and mortality reduction at 10 years of 18% and 10%, respectively. The authors noted that although the incidence and mortality reductions were clinically important, they were lower than anticipated based on observational and modelling studies.

The publication of the NordICC trial results induced media attention and controversy regarding the effectiveness of colonoscopies. Experts advised people to interpret the results cautiously, noting aspects of the NordICC trial that could contribute to the underwhelming findings. A critical issue was the low screening uptake (42%). In the adjusted per-protocol analyses, which compared participants not offered screening to those offered screening who received colonoscopy, incidence and mortality reductions at 10 years increased to 31% and 50%, respectively. Another important consideration was the relatively short 10-year follow-up period. This study aimed to evaluate whether the NordICC trial results are lower than expected based on modelling and to what extent the results could be explained by screening uptake and follow-up period.