Several studies have demonstrated that snare tip soft coagulation (STSC) of the resection margins can significantly reduce recurrence rates after conventional piecemeal endoscopic mucosal resection (EMR). However, there is a lack of data regarding the efficacy of STSC in the context of piecemeal underwater EMR (pU-EMR) of large (≥20 mm) nonpedunculated colorectal polyps (LNPCPs).

This study aimed to assess the impact on recurrence rates of thermal ablation of the resection margins following pU-EMR. We conducted a retrospective single-center study including all LNPCPs removed by pU-EMR between 2022 and 2024. The primary outcome was endoscopic recurrence at follow-up colonoscopy. Adverse events, including bleeding and perforation, were also recorded.

Among 55 LNPCPs resected by pU-EMR (54 patients), 33 lesions underwent follow-up colonoscopy and were included in the analysis (median size, 25 mm; interquartile range, 25–45 mm; right colon location, 57.6%). Of these, 25 lesions (75.8%) received STSC of the resection margins. At follow-up colonoscopy (median interval, 6 months; interquartile range, 5–7 months), no recurrence was observed in the non-STSC group (0/8), while a single recurrence occurred in the STSC group (1/25; 4.0%). No adverse events were reported. The isolated recurrence was effectively managed with repeat endoscopic resection.

Recurrence after pU-EMR was rare overall and notably absent in lesions that did not undergo margin ablation. These findings suggest that, unlike conventional EMR, routine snare tip soft coagulation may not be necessary in the underwater setting. Given the small sample size and low event rate, prospective studies with larger cohorts are warranted to determine the true role of thermal margin ablation after pU-EMR.