STER Demonstrates Strong Real-World Outcomes for Upper GI Subepithelial Tumors : Gastrointest Endosc | May 2026

Introduction

Submucosal Tunneling Endoscopic Resection has emerged as an important minimally invasive approach for management of upper gastrointestinal Subepithelial Tumors arising from or closely associated with the muscularis propria layer. Although extensive Asian experience has established the efficacy of STER, Western outcome data have remained limited, particularly regarding technical feasibility, fibrosis-related complexity and transmural resection requirements.

Problem Statement

Real-world U.S. data evaluating procedural success, adverse events and predictors of technical difficulty during STER for upper gastrointestinal subepithelial lesions are sparse. In particular, factors influencing transmural resection and incomplete resection remain poorly characterized.

Summary

This multicenter U.S. retrospective study evaluated outcomes of STER across eight tertiary centers for upper gastrointestinal subepithelial lesions originating from or inseparable from the muscularis propria layer. Most lesions had undergone prior diagnostic sampling before referral, and suspected gastrointestinal stromal tumors represented a major indication for intervention.

STER achieved excellent technical outcomes, with en bloc resection and successful specimen retrieval in more than 94% of lesions. Importantly, no recurrences were observed during follow-up, supporting the oncologic adequacy and durability of endoscopic resection in appropriately selected lesions.

A major finding was the impact of submucosal fibrosis on procedural complexity. Fibrosis was identified in nearly one-fifth of lesions and was universally associated with prior tissue sampling. Fibrotic lesions were substantially more likely to require transmural resection, highlighting how repeated biopsy or EUS-guided sampling may alter tissue planes and compromise technical ease of definitive endoscopic therapy.

Gastrointestinal Stromal Tumor histology and extraluminal extension were also strongly associated with transmural resection requirements. These lesions likely reflect deeper muscular involvement and distorted anatomic planes, increasing procedural complexity and the need for full-thickness dissection.

Importantly, although transmural resection prolonged procedure duration and increased R1 resection rates, it did not significantly increase adverse events. Most complications were managed conservatively, supporting the relative safety of advanced third-space endoscopic techniques in experienced centers.

The study has several important practical implications for therapeutic endoscopy. First, it reinforces STER as an effective organ-preserving alternative to surgery for selected upper GI subepithelial tumors, particularly in lesions arising from the muscularis propria layer. Preservation of mucosal integrity through the tunneling approach likely contributes to reduced leak risk and faster recovery compared with exposed full-thickness techniques.

Second, the findings challenge the routine use of extensive pre-resection tissue acquisition in lesions already strongly suspected to represent resectable GISTs or symptomatic muscularis propria tumors. Excessive prior sampling may induce fibrosis that complicates subsequent definitive resection without necessarily improving management decisions.

The work also highlights the increasing sophistication of third-space endoscopy within Western practice. Historically concentrated in high-volume Asian centers, advanced submucosal tunneling techniques are now demonstrating reproducible safety and efficacy across U.S. tertiary institutions.

Clinically, optimal patient selection remains critical. Lesions with extraluminal growth, deep muscular attachment or prior fibrosis may require advanced expertise and longer procedural planning. Nevertheless, even these technically challenging cases remained manageable endoscopically in experienced hands.

Overall, this multicenter U.S. experience demonstrates that STER is a safe, effective and durable minimally invasive approach for selected upper gastrointestinal subepithelial tumors. The study additionally identifies prior sampling-induced fibrosis, GIST histology and extraluminal extension as key predictors of transmural resection complexity, emphasizing the importance of procedural planning and careful diagnostic sequencing.