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Screening colonoscopy versus sigmoidoscopy: implications of a negative examination for cancer prevention and racial
Bechien U Wu1, George F Longstreth2, Eunis W Ngor3
1Center for Digestive Health Research, Southern California Permanente Medical Group, Los Angeles, California, USA; Division of Gastroenterology, Kaiser Permanente Los Angeles Medical Center, Los Angeles, California, USA.
Background:
Both colonoscopy and flexible sigmoidoscopy are accepted procedures for colorectal cancer (CRC) screening in the United States.
Objective:
To compare risk of CRC after negative findings on screening colonoscopy versus sigmoidoscopy and to evaluate racial/ethnic disparities in postscreening CRC.
Design:
Retrospective, comparative cohort study.
Setting:
Integrated community-based health-care system.
Patients:
Average-risk patients 50 to 75 years of age with negative findings on an initial endoscopic screening examination from January 2000 to December 2010.
Interventions:
Colonoscopy versus sigmoidoscopy as the initial screening procedure.
Main Outcome Measurements:
Incident cases of CRC identified via a prospective internal cancer registry, risk of CRC determined by Cox regression adjusted for age, sex, race/ethnicity, and comorbidity.
Results:
The study cohort included 138,297 patients (42,938 patients with negative findings on colonoscopy and 95,359 with negative findings on sigmoidoscopy). The median age was 57.9 years (interquartile range 53.0-64.1 years). Women comprised 51.8% of the cohort with 42.2% non-Hispanic white patients, 24.1% Hispanic patients, 10.7% non-Hispanic black patients, 9.7% Asian patients, and 13.3% other/unknown. A total of 241 cases of CRC was detected during 553,543 person-years of follow-up. The adjusted hazard ratio (HR) of postscreening CRC was 0.42 (95% confidence interval [CI], 0.28-0.64; P < .0001) for colonoscopy versus sigmoidoscopy. Risk reduction was primarily among proximal tumors (adjusted HR 0.30; 95% CI, 0.16-0.57). Non-Hispanic black patients were at higher risk of postscreening CRC compared with non-Hispanic white patients (adjusted HR 1.71; 95% CI, 1.20-2.42); however, this disparity was noted only in the sigmoidoscopy cohort.
Limitations:
Retrospective study with potential selection bias and residual confounding.
Conclusions:
Negative screening colonoscopy was associated with decreased incidence of subsequent CRC and a decrease in disparities compared with negative sigmoidoscopy findings in this large, community-based setting.
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