Large serrated polyps indicate a greater risk of advanced metachronous colorectal neoplasia than high-grade adenomas

Background and study aims The risk of developing total metachronous advanced neoplasia (TMAN) in patients with index serrated lesions (SL) or adenoma with high-grade dysplasia (HGD) is unknown. We evaluated this risk in patients with either HGD, SL < 10 mm or SL = 10 mm at index colonoscopy, who underwent surveillance colonoscopies.Patients and methods This retrospective cohort study evaluated all consecutive patients (n = 2477) diagnosed between 2010 and 2019 with colorectal HGD, SLs < 10 mm or SLs = 10 mm. We excluded patients aged < 45 or > 75 years or those who had inflammatory bowel disease, hereditary colorectal cancer (CRC) syndromes, previous or synchronous CRC, or no follow-up colonoscopy. Descriptive variables were compared using analysis of variance or Pearson chi-squared tests. Multivariate Cox regressions were used to compare the risk of TMAN between the HGD, SL < 10 mm and SL = 10 mm groups.Results Overall, 585 patients (mean age 63 years; 55% male; mean follow-up 3.67 years) were included (226 with SLs < 10 mm, 204 with SLs = 10 mm, 155 with HGD). Compared with SLs < 10 mm, patients with HGD did not have a significantly different rate of TMAN (HR= 0.75 [0.39- 1.44]) and patients with SLs = 10 mm had a higher rate of TMAN (HR= 2.08 [1.38-3.15]). Compared with HGD, patients with SLs = 10 mm had a higher rate of TMAN (HR= 1.87 [1.04-3.36]).Conclusions The risk for TMAN was higher for patients with SLs = 10 mm than with HGD or SLs < 10 mm. This risk should be considered when planning surveillance intervals for patients diagnosed with large SLs.