Heterogeneity in colorectal cancer incidence among people recommended 3-yearly surveillance post-polypectomy: a validation study

Background Colonoscopy surveillance is recommended for patients at increased risk of colorectal cancer (CRC) following adenoma removal. Low-, intermediate-, and high-risk groups are defined by baseline adenoma characteristics. We previously evaluated surveillance in intermediate-risk patients using UK hospital data, identifying a higher-risk subgroup who benefitted from surveillance and a lower-risk subgroup who may not require surveillance. Here we explored whether these findings apply in individuals undergoing CRC screening. Methods Retrospective study using data from the UK Flexible Sigmoidoscopy Screening Trial (UKFSST), English CRC screening pilot (ECP), and US Kaiser Permanente CRC prevention programme (KPCP). Screening participants aged 50–74 years and classed as intermediate-risk at baseline colonoscopy were included. CRC data were available through 2006 (KPCP) or 2014 (UKFSST, ECP). We classified participants into lower- and higher-risk subgroups using our previously identified baseline risk factors; higher-risk participants were those with incomplete colonoscopies, poor bowel preparation, adenomas ≥20mm or with high-grade dysplasia, or proximal polyps. We compared CRC incidence rates in these subgroups and in the presence versus absence of surveillance using Cox regression. Results Of 2291 intermediate-risk participants, 45% were classified as higher-risk. Median follow-up was 11.8 years. CRC incidence rates were significantly higher in the higher-risk than lower-risk subgroup (hazard ratio [HR]=2.08, 95%CI 1.07–4.06). Surveillance reduced CRC incidence rates in higher-risk participants (HR=0.35, 0.14–0.86), but not statistically significantly so in lower-risk participants (HR=0.41, 0.12–1.38). Conclusion As previously demonstrated for hospital patients, screening participants classed as intermediate-risk comprise two risk subgroups. Surveillance clearly benefits the higher-risk subgroup