Objective Postpolypectomy surveillance guidelines for colorectal cancer introduced the concept of ‘risk stratification’; however, few studies have been conducted for validation of its usefulness. The aim of this study was to assess the 5-year incidence of advanced neoplasia recurrence based on the risk stratification scheme of the guidelines and to identify its risk factors.

Methods A prospective study of surveillance colonoscopy after screening colonoscopy was carried out at the Seoul National University Hospital Healthcare System Gangnam Center. 3803 asymptomatic Koreans aged 50–69 were enrolled prospectively and 5-year cumulative adenoma rates were analysed according to three risk groups: normal (no baseline adenoma), low-risk (1–2 adenomas <10 mm) and high-risk (an advanced adenoma or ≥3 adenomas) groups. The RR was computed by HR using Cox proportional regression after multivariate adjustments. The primary outcome was the 5-year cumulative rate of recurrent advanced adenoma in each risk category and the secondary outcome was its predictive factors.

Results Among 3803 subjects enrolled between 2003 and 2005, 2452 were followed-up within 5 years: 1242, 671 and 539 in the normal, low-risk and high-risk groups, respectively. Compared with the normal group, the low-risk group had a sufficiently low 5-year incidence and did not show an increased risk for subsequent advanced adenoma (2.4% vs 2.0%, HR=1.14, 95% CI 0.61 to 2.17). Conversely, a significantly higher 5-year rate (12.2%) and early recurrence (4.6, 7.4 and 9.6% at 1, 2 and 3 years) of advanced adenoma were revealed in the high-risk group. Among various patients and adenoma characteristics, only high-risk adenoma (HR=5.95, 95% CI 3.66 to 9.68) along with a number of ≥3 (HR=3.06, 95% CI 1.51 to 6.57) and size ≥10 mm (HR=3.02, 95% CI 1.80 to 5.06) were independent predictors.

Conclusions The surveillance interval for low-risk patients could be extended beyond 5 years. Colonoscopic surveillance should be targeted to high-risk patients, and 3-year follow-up after initial polypectomy may be appropriate.