Underwater vs. Conventional EMR of Large Nonpedunculated Colorectal Lesions: A Multicenter Randomized Controlled Trial

Published:December 23, 2022DOI:
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      Background & Aims

      Underwater endoscopic mucosal resection (UEMR) is an alternative procedure to conventional endoscopic mucosal resection (CEMR) to treat large nonpedunculated colorectal polyps (LNPCL). In this multicenter randomized clinical trial, we aimed to compare the efficacy and safety of UEMR versus CEMR on LNPCL.


      We conducted a multicenter randomized controlled clinical trial from February 2018 to February 2020 in 11 hospitals in Spain. A total of 298 patients (311 lesions) were randomized to the UEMR (n=149) and CEMR (n=162) groups. The main outcome was the lesion recurrence rate in at least one follow-up colonoscopy. Secondary outcomes included technical aspects, en bloc resection rate, R0 and adverse events, among others.


      There were no differences in the overall recurrence rate [9.5% UEMR vs. 11.7% CEMR; absolute risk difference -2.2% (CI 95%: -9.4% to 4.9%)]. However, considering the polyp sizes between 20 and 30 mm, the recurrence rate was lower for UEMR [3.4% UEMR vs. 13.1% CEMR; absolute risk difference -9.7% (CI 95%: -19.4% to 0%)]. The R0 resection showed the same tendency, with significant differences favoring UEMR only for polyps between 20 and 30 mm. Overall, UEMR was faster and easier to perform than CEMR. Importantly, both techniques were equally safe.


      UEMR is a valid alternative to CEMR of LNPCL and could be considered the first option of treatment for lesions between 20-30 mm due to its higher en bloc and R0 resection rates.

      Graphical abstract



      AEs (Adverse events), ASA (American Society of Anesthesiologists), ARD (Absolute risk difference), CEMR (Conventional mucosal endoscopic resection), CI (Confidence interval), EMR (Mucosal endoscopic resection), ESD (Endoscopic submucosal dissection), HGD (High-grade dysplasia), IQR (Interquartile range), ITT (Intention-to-treat), JNET (Japan NBI Expert Team), LGD (Low-grade dysplasia), LNPCL (Large nonpedunculated colonic lesions), LST (Laterally spreading tumors), NBI (Narrow band imaging), NICE (NBI international colorectal endoscopic), OR (Odds ratio), PP (per-protocol), PPS (Postpolypectomy syndrome), SD (Standard deviation), SEED (Spanish Society of Digestive Endoscopy), TC (Transverse colon), UEMR ("Underwater" mucosal endoscopic resection)
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