AbstractBackgroundAfter colorectal polypectomy, 20–50 per cent of patients develop metachronous polyps and some have increased colorectal cancer risk. British Society of Gastroenterology (BSG) 2020 guidelines recommend surveillance colonoscopy for high-risk patients based on index pathology. The aim of this study was to evaluate metachronous lesion outcome using BSG 2020 criteria.MethodsA retrospective, multicentred study was conducted including patients who had polypectomy during screening colonoscopy (2009–2016) followed by surveillance. Demographics, index pathology, and BSG 2020 risk criteria were compared with regard to metachronous lesion pathology (non-advancedversusadvanced lesions) and timing of detection (earlyversuslate). Advanced lesions were defined as adenomas/serrated polyps greater than or equal to 10 mm, high-grade dysplasia, serrated polyps with dysplasia, or colorectal cancer, and late lesions those detected greater than 2 years after the index procedure.ResultsOf 3090 eligible patients, 2643 were included. Among these, retrospective BSG 2020 application would have excluded 51.5 per cent from surveillance. After a median of 36 months, the advanced polyp/colorectal cancer rate in BSG 2020 high-risk patients was 16.3versus13.0 per cent in low-risk patients. Older age (P= 0.008) correlated with advanced metachronous lesions. Male sex, greater than five polyps, and BSG 2020 high-risk criteria correlated with non-advanced and advanced lesions (P< 0.001). Older age (P< 0.001), villous features (P= 0.006), advanced index polyp (P= 0.020), and greater than five polyps (P< 0.001) correlated with early metachronous lesions. Male sex and BSG 2020 high-risk criteria correlated with early and late lesions (P< 0.001). On multivariable regression, increased polyp number (odds ratio (OR) 1.15 (95 per cent c.i. 1.07 to 1.25);P< 0.001) and villous features (OR 1.49 (95 per cent c.i. 1.05 to 2.10);P= 0.025) independently correlated with early advanced lesions. The rate of non-advanced and advanced metachronous polyps was higher in BSG 2020 high-versuslow-risk patients (44.4versus35.4 per cent for non-advanced and 15.7versus11.8 per cent for advanced;P< 0.001), but the colorectal cancer rate was similar (0.6versus1.2 per cent). However, when examining only lesions detected greater than 2 years after the index colonoscopy in high-versuslow-risk patients, no significant differences were observed (P= 0.140).ConclusionBSG 2020 criteria correlated with metachronous polyps, but did not differentiate advanced and non-advanced lesions and were not predictive of late lesions.