Long-term risk of colorectal cancer by gender after positive colonoscopy: population-based cohort study.

BACKGROUND Evidence for surveillance intervals of colonoscopy are primarily based on adenoma recurrence rate rather than on colorectal cancer (C.R.C.) incidence. Little is known about long-term risk of C.R.C. after positive colonoscopy. In view of men have significantly higher C.R.C. risk than women, we aimed to estimate the gender-specific C.R.C. incidence after positive colonoscopy (adenoma or malignant lesion) at follow-up colonoscopy. METHODS 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 was reviewed. Multivariable Weibull regression models were used to estimate the incidence of C.R.C. at follow-up colonoscopy for subjects who were assigned a stratified risk level. The benchmark risk was defined according to a national survey. RESULTS The interval incidence of C.R.C. at a 10 year follow-up was 164 (95% C.I. 63-343) and 79 (95% C.I. 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 C.R.C. history, and in 7-8 years if they only had familial C.R.C. HISTORY Women had a lower risk of C.R.C., and reached a same risk level 3-5 years later than men. Coexisting above risk factors resulted in a sharp increase in the incidence of C.R.C. at follow-up exceeding the benchmark much earlier. CONCLUSION Surveillance intervals for men based on incidence of C.R.C. are in line with that recommended by the current guidelines for colonoscopy. However, an 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.