Supplementary Material for: Comparison of Therapeutic Outcomes Between Underwater EMR and Cap-Assisted EMR for Superficial Non-Ampullary Duodenal Epithelial Tumors Measuring 6~20 mm

Introduction:
Conventional endoscopic mucosal resection (EMR) is widely accepted for 6–20 mm superficial non-ampullary duodenal epithelial tumors (SNADETs); however, its en bloc and R0 resection rates remain suboptimal. Modified techniques, such as underwater EMR (UEMR) and cap-assisted EMR (EMRC), have been introduced to improve outcomes; nevertheless, comparative data are limited despite both techniques being increasingly utilized.
Methods:
This retrospective two-center study included patients with 6–20 mm SNADETs treated with either UEMR or EMRC between April 2016 and May 2024 at Kobe University Hospital and the International Clinical Cancer Research Center. Clinicopathologic characteristics, therapeutic outcomes, and adverse events were compared. Multivariate logistic regression analysis was conducted to identify risk factors for non-R0 and piecemeal resection.
Results:
A total of 155 SNADETs (51 UEMR, 104 EMRC) were included. The EMRC group achieved significantly higher R0 resection rates (86.5% vs. 62.7%; p < 0.001) and en bloc resection rates (94.2% vs. 78.4%; p = 0.003) without increasing adverse events. Multivariate analysis identified UEMR, lesion size ≥ 10 mm, anterior or lateral wall involvement as independent risk factors for non-R0 resection. Lesion size ≥10 mm was the only independent risk factor for piecemeal resection.
Conclusion:
In SNADETs measuring 6–20 mm, EMRC demonstrated higher en bloc and R0 resection rates than UEMR with a comparable safety profile, suggesting EMRC may be a useful option for achieving complete resection in selected cases. Prospective studies are needed to refine techniques to minimize complications while maintaining efficacy and to clarify long-term outcomes and recurrence.