Understanding the Results of a Randomized Trial of Screening Colonoscopy

Editorial in The New England Journal of Medicine:

For more than two decades, colonoscopy has been recommended as one of several available options for colorectal cancer screening, and it has been the predominant form of screening for colorectal cancer used in the United States. However, the best evidence to support its use has been limited to data from cohort studies, which have estimated that this type of screening has been associated with a 40 to 69% decrease in the incidence of colorectal cancer and a 29 to 88% decrease in the risk of death from this disease.1 Unlike randomized, controlled trials, which have provided support for fecal occult blood testing and sigmoidoscopy,2 cohort studies probably overestimate the real-world effectiveness of colonoscopy because of the inability to adjust for important factors such as incomplete adherence to testing and the tendency of healthier persons to seek preventive care.

This evidence gap is addressed by the landmark Nordic-European Initiative on Colorectal Cancer (NordICC) trial, the results of which are now reported in the Journal by Bretthauer et al.3 This pragmatic trial involved nearly 85,000 men and women who were randomly assigned either to receive an invitation to undergo screening colonoscopy or to receive usual care (i.e., no screening). In the intention-to-screen analysis, colonoscopy was found to reduce the risk of colorectal cancer over a period of 10 years by 18% (risk ratio, 0.82; 95% confidence interval [CI], 0.70 to 0.93). However, the reduction in the risk of death from colorectal cancer was not significant (risk ratio, 0.90; 95% CI, 0.64 to 1.16).

More here.