Background and Aims: We investigated whether a diagnosis of colonic diverticular disease is associated with an increased risk for subsequent development of colorectal cancer (CRC) in a nationwide population-based retrospective study. Methods: We identified 41,359 individuals diagnosed with colonic diverticular disease as inpatients from 2000 through 2009 from the Taiwan National Health Insurance Research Database (study cohort) and collected data for 165,436 randomly selected additional subjects, matched by sex, age, and baseline year (comparison cohort). Data were collected until individuals developed CRC or withdrew from the National Health Insurance system, or until December 31, 2010. Cumulative incidences and hazard ratios (HRs) of CRC development were determined. To assess for ascertainment bias, we conducted an analysis excluding the first 12 months of follow-up evaluation. Results: The risk of CRC was significantly higher in the study cohort than in the comparison cohort (HR adjusted for age, sex, and comorbidities, 4.54; 95% confidence interval, 4.19-4.91; P < .0001). In a sensitivity analysis, we excluded the first 12 months of follow-up evaluation after a diagnosis of colonic diverticular disease; subsequent incidence rates for CRC in the study and comparison cohorts were 15.13 and 15.74 per 10,000 person-years, respectively (adjusted HR, 0.96; 95% confidence interval, 0.83-1.11). Conclusions: Colonic diverticular disease is not associated with an increased risk of subsequent CRC after the first year of diagnosis of colonic diverticular disease. An increased risk was observed in the first year, possibly owing to misclassification and screening effects.
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