Curative value of underwater endoscopic mucosal resection for submucosally invasive colorectal cancer

Background and Aim Occasionally, colorectal tumors without characteristics of deep submucosal invasion are found to be invasive upon pathological evaluation after endoscopic resection (ER). Because the resection depth for underwater endoscopic mucosal resection (UEMR) has not been clarified, we evaluated the feasibility of UEMR for pathologically invasive colorectal cancer (pT1‐CRC). Methods We retrospectively investigated data on the backgrounds and outcomes of patients with pT1‐CRC who underwent UEMR between January 2014 and June 2019 at our institute. As a reference standard, the backgrounds and outcomes of pT1‐CRCs that had undergone conventional EMR (CEMR) were also investigated. Results Thirty‐one patients (median age, 68 years [range, 32–88 years]; 22 men [71%]) were treated with UEMR. Median lesion size was 17 mm (range, 6–50 mm). The endoscopic complete resection rate was 100%. The overall en bloc resection rate was 77%, and the VM0, HM0, and R0 resection rates were 81%, 58%, and 55%, respectively. In cases of pT1a (invasion