Accounting for differential exclusions in the Nordic-European initiative on colorectal cancer trial discloses stronger-than-reported effects of screening colonoscopy

Abstract

Objectives: Recently, results on colorectal cancer (CRC) incidence and mortality reduction by the offer of screening colonoscopy were reported for the first time from a randomized controlled trial (RCT), the Nordic-European Initiative on Colorectal Cancer (NordICC) trial. Despite randomization, there was a substantially lower proportion of postrandomization exclusions of CRC cases due to cancer registry-recorded date of diagnosis before recruitment in the invited group than in the usual-care group. We aimed to evaluate the impact of such differential exclusions on the trial's effect estimates on CRC risk. Study Design and Setting: We compared reported postrandomization exclusions of CRC cases due to cancer registry-recorded date of diagnosis, and we derived adjusted effect estimates on CRC risk accounting for the reported differential postrandomization exclusion of CRC cases in the invited group and the usual-care group. Results: Reported postrandomization exclusion proportions of CRC cases were originally reported as 52/31,472 (0.17%) and 159/63,133 (0.25%) in the invited and usual-care group, respectively, (P