Background and Aim

A multicenter randomized controlled trial (RCT) reported a better R0 resection rate for intermediate-sized (10–20 mm) colorectal polyps with underwater endoscopic mucosal resection (UEMR) than conventional endoscopic mucosal resection (CEMR). To clarify whether UEMR removes enough submucosal tissue in the removal of unpredictable invasive cancers, we investigated the cutting plane depth with UEMR versus CEMR.

Methods

This was a post hoc analysis of a RCT in which 210 intermediate-sized colorectal polyps were removed in five Japanese hospitals. One pathologist and two gastroenterologists independently reviewed all resected specimens and measured the cutting plane depth. The cutting plane depth was evaluated as: i) maximum depth of submucosal layer, ii) mean depth of submucosal layer, calculated using a virtual pathology system.

Results

We identified 168 appropriate specimens for the evaluation of the cutting plane depth, resected by UEMR (n = 88) and CEMR (n = 80). The median resection depth was not significantly different between UEMR and CEMR specimens, regardless of the measurement method [i) 1,317 vs. 1,290 μm, P = .52; ii) 619 vs. 545 μm, P = .32]. All specimens in the UEMR and CEMR groups contained substantial submucosa and no muscularis propria.

Conclusions

The cutting plane depth with UEMR was comparable to that with CEMR. UEMR can be a viable alternative method that adequately resects the submucosal layer for the histopathological assessment of unpredictable submucosal invasive cancers.