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

BACKGROUND AND AIMS 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 to 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 <1000 μm)-CRC (n=14), the en bloc, VM0, and R0 resection rates were 92%, 100%, and 71%, respectively. Seventeen patients (five with risk factors for lymph node metastasis and twelve without) were followed up, and no local recurrence and distant metastasis were observed during the follow-up period [median follow-up period, 18 months (range, 6-62 months)] after UEMR. The outcomes of UEMR seemed to be comparable to those of CEMR (n=32). CONCLUSIONS The VM0 rate of UEMR for pT1-CRC, especially for pT1a-CRC, without characteristics of deep submucosal invasion seems feasible.