• Geir Hoff, Tom Grotmol, Eva Skovlund, Michael Bretthauer, and Norwegian Colorectal Cancer Prevention Study Group.
• Norwegian Colorectal Cancer Prevention (NORCCAP) Centre, Cancer Registry of Norway, Montebello, NO-0310 Oslo, Norway. hofg@online.no
• BMJ. 2009 Jan 1;338:b1846.

ObjectiveTo determine the risk of colorectal cancer after screening with flexible sigmoidoscopy.DesignRandomised controlled trial.SettingPopulation based screening in two areas in Norway-city of Oslo and Telemark county (urban and mixed urban and rural populations).Participants55 736 men and women aged 55-64 years.InterventionOnce only flexible sigmoidoscopy screening with or without a single round of faecal occult blood testing (n=13 823) compared with no screening (n=41 913).Main Outcome MeasuresPlanned end points were cumulative incidence and mortality of colorectal cancer after 5, 10, and 15 years. This first report from the study presents cumulative incidence after 7 years of follow-up and hazard ratio for mortality after 6 years.ResultsNo difference was found in the 7 year cumulative incidence of colorectal cancer between the screening and control groups (134.5 v 131.9 cases per 100 000 person years). In intention to screen analysis, a trend towards reduced colorectal cancer mortality was found (hazard ratio 0.73, 95% confidence interval 0.47 to 1.13, P=0.16). For attenders compared with controls, a statistically significant reduction in mortality was apparent for both total colorectal cancer (hazard ratio 0.41, 0.21 to 0.82, P=0.011) and rectosigmoidal cancer (0.24, 0.08 to 0.76, P=0.016).ConclusionsA reduction in incidence of colorectal cancer with flexible sigmoidoscopy screening could not be shown after 7 years' follow-up. Mortality from colorectal cancer was not significantly reduced in the screening group but seemed to be lower for attenders, with a reduction of 59% for any location of colorectal cancer and 76% for rectosigmoidal cancer in per protocol analysis, an analysis prone to selection bias.Trial RegistrationClinical trials NCT00119912.

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