The influence of the surveillance time interval on the risk of advanced neoplasia after non-advanced adenoma removal.

Objectives: To investigate the incidence of advanced neoplasia (colorectal cancer or advanced adenoma) at surveillance colonoscopy following removal of non-advanced adenoma; to determine whether the time interval before surveillance colonoscopy influences the likelihood of advanced neoplasia.

Design: Retrospective cohort study.

Setting, Participants: Patients enrolled in a South Australian surveillance colonoscopy program with findings of non-advanced adenoma during 1999-2016 who subsequently underwent surveillance colonoscopy.

Main Outcome Measures: Incidence of advanced neoplasia at follow-up surveillance colonoscopy.

Results: Advanced neoplasia was detected in 169 of 965 eligible surveillance colonoscopies (18%) for 904 unique patients (median age, 62.0 years; interquartile range [IQR], 54.0-69.0 years), of whom 570 were men (59.1%). The median interval between the initial and surveillance procedures was 5.2 years (IQR, 4.4-6.0 years; range, 2.0-14 years). Factors associated with increased risk of advanced neoplasia at follow-up included age (per year: odds ratio [OR], 1.03; 95% CI, 1.01-1.05), prior history of adenoma (OR, 1.48; 95% CI, 1.01-2.15), two non-advanced adenomas identified at baseline procedure (v one: OR, 1.74; 95% CI, 1.18-2.57), and time to surveillance colonoscopy (OR, 1.21; 95% CI, 1.08-1.37). The estimated incidence of advanced neoplasia was 19% five years after non-advanced adenoma removal, and 30% at ten years.

Conclusions: Increasing the surveillance colonoscopy interval beyond five years after removal of non-advanced adenoma increases the risk of detection of advanced neoplasia at follow-up colonoscopy.