Evidence comparing the ability of conventional endoscopic mucosal resection (CEMR) and underwater EMR (UEMR) to achieve sufficient resection depth in colorectal tumors remains limited. To address this question, a Japanese randomized clinical trial compared resection depth between CEMR and UEMR in 217 patients with colorectal tumors measuring 10 to 20 mm. The mean resection depth was greater with UEMR than with CEMR (1,688.9 µm vs 1,432.3 µm), although the difference was not statistically significant (256.6 µm; 95% CI, -119.9 to 633.1 µm; p = 0.18).

Subgroup analyses showed that UEMR achieved significantly greater resection depths in the cecum and ascending colon (1,822.4 µm vs 1,096.5 µm) and in lesions with superficial morphology (1,238.7 µm vs 731.6 µm) than CEMR. Notably, nonexpert operators also achieved deeper resections with UEMR than with CEMR (1,786.6 µm vs 1,192.4 µm). Overall,…