Low risk of local recurrence after a successful en bloc Endoscopic Submucosal Dissection for non-invasive colorectal lesions with positive horizontal resection margins(R-ESD study).

Background During endoscopic submucosal dissection (ESD), normal mucosa is cut under constant optical control. We studied whether a positive horizontal resection margin after a complete en bloc ESD predicts local recurrence. Methods In this European multicenter cohort study, patients with a complete en bloc colorectal ESD were selected from prospective registries. Cases were defined by a horizontal resection margin positive or indeterminate for dysplasia (HM1), whereas controls had a free resection margin (HM0). Low-risk lesions with submucosal invasion (T1) and margins free of carcinoma were analysed seperately. The main outcome was local recurrence. Results From 928 consecutive ESDs (2011-2020), 354 patients (40% female, mean age 67 years, median follow-up 23.6 months) were included concerning 308 non-invasive lesions and 46 T1 lesions. Recurrence rate for non-invasive lesions was 1/212 (0.5%; 95%CI 0.02-2.6%) for HM0 vs. 2/96 (2.1%; 95%CI 0.57-7.3%) for HM1. Recurrence rate for T1 was 1/38 (2.6%; 95%CI 0.14-13.5%) for HM0 vs. 2/8 (25%; 95%CI 7.2-59%) for HM1. Conclusion A positive horizontal resection margin after an en bloc ESD for non-invasive lesions is associated with a marginal non-significant increase of the local recurrence rate, equal to an ESD with clear horizontal margins. This could not be confirmed for T1 lesions.