Underwater Endoscopic Mucosal Resection Is a Technique with a Short Learning Curve: A Multicentric Prospective Study.

Introduction and Aims: Underwater endoscopic mucosal resection (U-EMR) emerged as a promising alternative to conventional EMR (C-EMR) for resecting large colorectal polyps. There is a lack of studies focusing on its learning curve. Thus, we aimed to determine the learning curve of U-EMR in endoscopists without prior experience in U-EMR. Methods: Four endoscopists from 4 different centers performed U-EMR after standardized online training. Patients with non-pedunculated colorectal lesions sized 10-30 mm were enrolled between November 2023 and June 2024. The primary outcome was to evaluate technical success, en bloc resection rates, procedural time, and adverse events before and after 10 and 15 procedures, to assess whether this threshold is sufficient for proficiency. Results: Overall, 84 lesions were included, median size of 17 mm [10-35 mm]. Mean procedural time was 3.99 min, with an average of 1.21 piecemeal fragments per lesion, and en bloc resection rate was 85%, with all lesions completely resected. When comparing learning phases, en bloc resection rates were 83.3% in the first period (first 15 lesions) and 87.5% thereafter, with a slight reduction in mean procedural time (4.13 vs. 3.77 min). There were no significant differences in procedural time or en bloc resection when comparing results after 10 or 15 procedures, no observed improvements after the 16th procedure. No perforations, delayed bleeding, or hospital admissions occurred. Intraprocedural bleeding occurred in 3.6% of cases and was managed conservatively. Prophylactic clip closure was performed in 34.5% of cases, primarily in the right colon. Conclusion: U-EMR is safe, efficient, and easily adopted, with proficiency that may be achieved after a small number of procedures.