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PLoS One. 2019 Dec 5;14(12):e0226027. doi: 10.1371/journal.pone.0226027. eCollection 2019.

Screening colonoscopy and flexible sigmoidoscopy for reduction of colorectal cancer incidence: A case-control study.

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Division of Gastroenterology, Department of Medicine, University of Washington School of Medicine, Seattle, Washington, United States of America.
National Cancer Institute, National Institutes of Health, Bethesda, Maryland, United States of America.
Information Management Services, Inc., Calverton, Maryland, United States of America.
Kaiser Permanente Washington Health Research Institute, Seattle, Washington, United States of America.
Department of Epidemiology, University of Washington, Seattle, Washington, United States of America.



Flexible sigmoidoscopy and colonoscopy are both recommended colorectal cancer screening options, but their relative effectiveness needs clarification. The aim of this study was to compare the effectiveness of colonoscopy and flexible sigmoidoscopy for reduction of colorectal cancer incidence.


We conducted a case-control study within the linked Surveillance, Epidemiology, and End Results (SEER)-Medicare database. Cases were subjects age 70-85 years in the SEER-Medicare database diagnosed with CRC during 2004-2013. Up to 3 controls were matched to each case by birth year, sex, race, and SEER region. Receipt of screening colonoscopy or flexible sigmoidoscopy was ascertained from Medicare claims. Conditional logistic regression models were developed to estimate the odds ratios (ORs) and 95% confidence intervals (CI) for a history of screening in cases vs. controls. We conducted secondary analyses by sex, race, endoscopist characteristics, and with varying timing and duration of the look-back period.


Receipt of screening colonoscopy and sigmoidoscopy was associated with a 59% (OR 0.41, 95%CI 0.39, 0.43) and 22% reduction (OR 0.78, 95%CI 0.67, 0.92) in colorectal cancer incidence, respectively. Colonoscopy was associated with greater reduction in the distal colorectal cancer incidence (OR 0.22, 95%CI 0.20, 0.24) than proximal colorectal cancer incidence (OR 0.62, 95%CI 0.59, 0.66). Sigmoidoscopy was associated with a 52% reduction in distal colorectal cancer incidence (OR 0.48, 95%CI 0.37, 0.63), but with no reduction in proximal colorectal cancer incidence. These associations were stronger in men than in women. No differences by race or endoscopist characteristics were observed.


Both screening colonoscopy and sigmoidoscopy were associated with reductions in overall colorectal cancer incidence, with a greater magnitude of reduction observed with colonoscopy.

Conflict of interest statement

Michael J. Barrett is an employee of Information Management Systems, Inc., the information technology contractor of the National Cancer Institute. This company assists researchers with creation of SEER-Medicare data files and assistance with data analyses, and does not have a commercial interest in any products or publications resulting from this database. This commercial affiliation does not alter adherence to all PLOS ONE policies on sharing data and materials.

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