Efficacy of Underwater Endoscopic Mucosal Resection

Intestinal polyps
Computer illustration of polyps in the intestine. Polyps are small benign (non-cancerous) growths that arise from the mucus lining of the intestine. Polyps should be surgically removed as they may become malignant (cancerous).
Investigators aimed to determine whether UEMR is superior to CEMR for the treatment of large, sessile or flat colorectal polyps.

Colorectal polyps removed via underwater endoscopic mucosal resection (UEMR) had a higher rate of en bloc resection and a lower rate of recurrence compared with polyps removed via conventional endoscopic mucosal resection (CEMR), according to the results of a study published in Gastroenterology.

While CEMR is considered the current standard for treatment of large colorectal polyps, it is associated with low rates of en bloc resection and potential adenoma recurrence. A need for a resection technique that is superior to CEMR, without leading to high rates of adverse events, is imperative. For these reasons, investigators aimed to determine whether UEMR is superior to CEMR for the treatment of large, sessile or flat colorectal polyps.  

The randomized, prospective clinical trial enrolled 147 patients with 158 sessile or flat colorectal lesions that ranged from 20 mm to 40 mm in size. Lesions were randomized 1:1 to be removed via UEMR or CEMR. All patients underwent a repeat colonoscopy at 6 months to assess for recurrence.

The primary endpoint was the difference in the 6-month recurrence rate between the two treatment arms. Secondary outcomes included the en bloc resection rate, R0 resection rate, and adverse events.

The mean age of study participants was 67.2 years (SD, 10.8 years); 65.7% of participants were men. The median size of measured polyps was 25 mm.

The overall recurrence rate was marginally better in the UEMR group compared with the CEMR group, at 15.1% and 24.6%, respectively. However, this rate was not statistically significant (P =.253) The difference in recurrence rate was much more notable in the subgroup of lesions ranging from 30 mm to 40 mm in size, at 6.3% for UEMR and 42.9% for CEMR (P =.031). The en bloc resection and R0 resection rates were also higher in UEMR (33.3% and 32.1%) than in CEMR (18.4% and 15.8%), respectively. There was no significant difference in adverse events between both groups (P =.611).

This study had several limitations. Bias is possible, as endoscopists were not blinded to group allocation. Further, lesion size was estimated macroscopically, though previous research has indicated that endoscopists can overestimate lesion size by up to 20%. Finally, the single-center nature of this study may limit its generalizability.

UEMR demonstrated improved efficacy, with comparable safety and technique required. Investigators “consider UEMR to be an ideal technique for the resection of large benign colorectal polyps up to 40 mm in size.”

Disclosure: The authors declared affiliations with biotech, pharmaceutical, and/or device companies. Pleases see the original reference for a full list of author disclosures.


Nagl S, Ebigbo A, Goelder SK, et al. Underwater-versus conventional endoscopic mucosal resection of large sessile or flat colorectal polyps: a prospective randomized controlled trial. Gastroenterology. Published online August 6, 2021. doi: 10.1053/j.gastro.2021.07.044