Supplementary Material for: Underwater Clip Closure versus Conventional Clip Closure following Endoscopic Submucosal Dissection in Colorectal Lesions: A First Comparative Study

Introduction
This single-center retrospective study compared underwater clip closure (UCC) with conventional clip closure (CCC) under routine gas insufflation for post-endoscopic submucosal dissection (ESD) ulcers of colorectal lesions measuring ≤5 cm.

Methods
Between May 2021 and June 2023, 89 patients were enrolled. Since March 2022, all cases underwent UCC. Patients were divided into the UCC group (n = 52) and the CCC group (n = 37). Primary outcomes were complete closure rate and incidence of post-ESD coagulation syndrome (PECS), delayed bleeding, and perforation. Secondary outcomes included closure time and number of clips used.

Results
Complete closure was achieved in all cases, with no PECS, delayed bleeding, or perforation in either group. Median closure time was significantly shorter in the UCC group (10 min [IQR, 7–14]) than in the CCC group (11 min [IQR, 8.5–19]; p = 0.044). The number of clips used was similar (median 10 in both groups; p = 0.290). Multiple regression analysis identified both resection area (p < 0.001) and closure method (p = 0.002) as independent factors affecting closure time.

Conclusion
UCC may decrease the time required for post-ESD closure of colorectal lesions measuring ≤5 cm, while using a comparable number of clips to CCC, with no serious complications.