Objective:
Colonoscopy surveillance aims to reduce colorectal cancer (CRC) incidence post-polypectomy. The 2020 UK guidelines recommend surveillance at three years for ‘high-risk’ patients with ≥2 premalignant polyps (PMPs) of which ≥1 is ‘advanced’ (serrated polyp [or adenoma] ≥10mm or with [high-grade] dysplasia); ≥5 PMPs; or ≥1 non-pedunculated polyp ≥20mm; ‘low-risk’ patients without these findings are instead encouraged to participate in population-based CRC screening. We examined the appropriateness of these risk classification criteria and recommendations.

Design:
Retrospective analysis of patients who underwent colonoscopy and polypectomy mostly between 2000–2010 at 17 UK hospitals, followed-up through 2017. We examined CRC incidence by baseline characteristics, risk group, and number of surveillance visits using Cox regression, and compared incidence with that in the general population using standardised incidence ratios (SIRs).

Results:
Among 21,318 patients, 368 CRCs occurred during follow-up (median: 10.1 years). Baseline CRC risk factors included age ≥55 years, ≥2 PMPs, adenomas with tubulovillous/villous/unknown histology or high-grade dysplasia, proximal polyps, and a baseline visit spanning 2–90 days. Compared with the general population, CRC incidence without surveillance was higher among those with adenomas with high-grade dysplasia (SIR:1.74, 95%CI:1.21–2.42) or ≥2 PMPs of which ≥1 was advanced (1.39, 1.09–1.75). For low-risk (71%) and high-risk (29%) patients, SIRs without surveillance were 0.75 (95%CI:0.63–0.88) and 1.30 (1.03–1.62), respectively; for high-risk patients after first surveillance, the SIR was 1.22 (0.91–1.60).

Conclusion:
These guidelines accurately classify post-polypectomy patients into those at high-risk, for whom one surveillance colonoscopy appears appropriate, and those at low-risk who can be managed by non-invasive screening.