Attempted underwater en bloc resection for large (2-4 cm) colorectal laterally spreading tumors (with video).

To evaluate the feasibility and outcomes of attempted underwater en bloc resection (UEBR) of large colorectal laterally spreading tumors (LSTs).Prospective, observational study.Tertiary academic referral center.Fifty patients meeting the inclusion and exclusion criteria.Standardized UEBR technique involving attempted en bloc resection without submucosal injection by using a large 33-mm snare.Complete endoscopic en bloc resection, histologic complete resection, procedure time, adverse events, and follow-up data.Over 13 months, UEBR was attempted in 50 patients (median age, 68 years) with 53 LSTs 2 to 4 cm in size. The median LST size was 30 mm (range 20-40 mm). The median procedure and resection times were 38 minutes (range 17-87 minutes) and 3 minutes (range 1-32 minutes), respectively. Complete endoscopic en bloc resection with the 33-mm snare was successful in 29 of 53 lesions (55%). Of these, histology showed neoplasia-free margins in 79%. Final histology was tubular adenoma (n = 26), sessile serrated adenoma (n = 10), tubulovillous adenoma (n = 14), villous adenoma (n = 2), and intramucosal carcinoma (n = 1). Adverse events (4%) were delayed bleeding in 1 and abdominal pain in 1 patient each. There were no perforations. Forty patients with a total of 43 adenomas had follow-up colonoscopy with biopsies of the resection site after a median of 31 weeks (range 7-71 weeks) after resection. Residual adenoma was found in 2 of 43 (5%).Single-center, limited follow-up.On an intention-to-treat basis, complete endoscopic en bloc resection was achieved in 55% of lesions with complete histologic resection verified in 79% of the en bloc specimens. UEBR without submucosal injection appears safe. Refinements are needed to improve UEBR success rates.