Effect of Flexible Sigmoidoscopy Screening on Colorectal Cancer Incidence and Mortality A Randomized Clinical Trial

IMPORTANCE Colorectal cancer is a major health burden. Screening is recommended in many countries. OBJECTIVE To estimate the effectiveness of flexible sigmoidoscopy screening on colorectal cancer incidence and mortality in a population-based trial. DESIGN, SETTING, AND PARTICIPANTS Randomized clinical trial of 100 210 individuals aged 50 to 64 years, identified from the population of Oslo city and Telemark County, Norway. Screening was performed in 1999-2000 (55-64-year age group) and in 2001 (50-54-year age group), with follow-up ending December 31, 2011. Of those selected, 1415 were excluded due to prior colorectal cancer, emigration, or death, and 3 could not be traced in the population registry. INTERVENTIONS Participants randomized to the screening group were invited to undergo screening. Within the screening group, participants were randomized 1: 1 to receive once-only flexible sigmoidoscopy or combination of once-only flexible sigmoidoscopy and fecal occult blood testing (FOBT). Participants with positive screening test results (cancer, adenoma, polyp >= 10 mm, or positive FOBT) were offered colonoscopy. The control group received no intervention. MAIN OUTCOMES AND MEASURES Colorectal cancer incidence and mortality. RESULTS A total of 98 792 participants were included in the intention-to-screen analyses, of whom 78 220 comprised the control group and 20 572 comprised the screening group (10 283 randomized to receive a flexible sigmoidoscopy and 10 289 to receive flexible sigmoidoscopy and FOBT). Adherence with screening was 63%. After a median of 10.9 years, 71 participants died of colorectal cancer in the screening group vs 330 in the control group (31.4 vs 43.1 deaths per 100 000 person-years; absolute rate difference, 11.7 [95% CI, 3.0-20.4]; hazard ratio [HR], 0.73 [95% CI, 0.56-0.94]). Colorectal cancer was diagnosed in 253 participants in the screening group vs 1086 in the control group (112.6 vs 141.0 cases per 100 000 person-years; absolute rate difference, 28.4 [95% CI, 12.1-44.7]; HR, 0.80 [95% CI, 0.70-0.92]). Colorectal cancer incidence was reduced in both the 50-to 54-year age group (HR, 0.68; 95% CI, 0.49-0.94) and the 55-to 64-year age group (HR, 0.83; 95% CI, 0.71-0.96). There was no difference between the flexible sigmoidoscopy only vs the flexible sigmoidoscopy and FOBT screening groups. CONCLUSIONS AND RELEVANCE In Norway, once-only flexible sigmoidoscopy screening or flexible sigmoidoscopy and FOBT reduced colorectal cancer incidence and mortality on a population level compared with no screening. Screening was effective both in the 50-to 54-year and the 55-to 64-year age groups.