S5298 Surgery-Sparing Management of Gastric GISTs Using Submucosal Tunneling Endoscopic Resection: Experience From 2 Distinct Anatomical Presentations

Introduction: Gastrointestinal stromal tumors (GISTs) arising from the muscularis propria have traditionally required surgical intervention for management. However, tumors near the gastroesophageal (GE) junction or in anatomically complex areas pose technical challenges that may necessitate subtotal or total gastrectomy. Submucosal tunneling endoscopic resection (STER) offers a minimally invasive, organ-preserving alternative. We present 2 cases of gastric GISTs—1 near the GE junction and 1 in the mid-gastric body—successfully managed using STER. Case Description: A 69-year-old woman underwent magnetic resonance imaging for follow-up of a presumed pancreatic cyst, incidentally revealing a 2.5 cm mass at the lesser curvature near the GE junction. Endoscopic ultrasound (EUS) demonstrated a 2.1 × 1.8 cm hypoechoic lesion arising from the muscularis propria. Fine-needle biopsy (FNB) confirmed a spindle cell GIST (DOG1, desmin, caldesmin positive). Surgical oncology recommended near total gastrectomy, but the patient opted for STER. A submucosal tunnel was created 5 cm proximal to the lesion using a hybrid knife after methylene blue-saline injection. The mass was resected en bloc with traction-assisted dissection and retrieved using rat-tooth forceps. Mucosal entry was closed with through-the-scope clips. Pathology confirmed a 3.2 cm GIST with focal margin involvement likely due to retrieval artifact. No necrosis or high mitotic activity was noted. Case 2 is a 72-year-old man who was evaluated for a gastric lesion found during imaging for abdominal pain. EUS showed a 2.3 × 2 cm homogenous, hypoechoic mass with central anechoic area in the anterior gastric body. FNB revealed a mixed epithelioid and spindle cell GIST (C-KIT, DOG1 positive). STER was performed similarly. A Mantis clip and thread were used for traction, and myotomy was performed using an IT nano knife. The mass was retrieved with a rescue net. Pathology confirmed a 2.5 cm low-grade GIST with negative margins. Discussion: These cases demonstrate the feasibility and effectiveness of STER in managing gastric GISTs located in anatomically complex regions. STER enabled complete resection while preserving gastric anatomy and avoiding high-morbidity surgery. This approach may serve as a safe and durable alternative in carefully selected patients.