Long-term Risk of Colorectal Cancer by Gender after Positive Colonoscopy: Population-Based Cohort Study

<b>Background:</b> Evidence for surveillance intervals of colonoscopy are primarily based on adenoma recurrence rate rather than on colorectal cancer (CRC) incidence. Little is known about a long-term risk of CRC after positive colonoscopy. In view of men have significantly higher CRC risk than women, we aimed to estimate the gender-specific CRC incidence after positive colonoscopy (adenoma or malignant lesion) at follow-up colonoscopy. <b>Methods:</b> A retrospective cohort study was conducted using data from a database of colonoscopy screening and surveillance. Patients having had a colonoscopy (January 2010-March 2014) were selected as study subjects and the history of prior colonoscopies were reviewed. Multivariable Weibull regression models were used to estimate the incidence of CRC at follow-up colonoscopy for subjects who were assigned a stratified risk level. The benchmark risk was defined according to a national survey. <b>Results:</b> The interval incidence of CRC at a 10-year follow-up was 164 (95%CI 63-343) and 79 (95%CI 26-188) per 100,000 person-years for low-risk men and women respectively, which tallied with our benchmark risk. Men exceeded the benchmark risk in 3-5 years if they had an incomplete polyp removal, ≥3 adenomas during their last colonoscopy or a personal CRC history, while in 7-8 years if only they had a familial CRC history. Women had a lower risk of CRC, and reached a same risk level in 3-5 years later than men. Coexisting above risk factors resulted in a sharp increase in the incidence of CRC at follow-up exceeding the benchmark much earlier. <b>Conclusion:</b> Surveillance intervals for men based on incidence of CRC are in line with that recommended by the current guidelines for colonoscopy. But, an additional extension of 3-5 years may be appropriate for women. To target personalized medicine, a risk predictive model could be used to identify an appropriate surveillance interval for each individual in the future.