NOVEL ENDOSCOPIC ONCOLOGY: EN BLOC REMOVAL OF LARGE GASTRIC GASTROINTESTINAL STROMAL TUMOR (GIST) WITH SUBMUCOSAL TUNNEL ENDOSCOPIC RESECTION (STER) FOLLOWING NEOADJUVANT THERAPY

Introduction:
Gastrointestinal stromal tumors (GISTs) are the most common mesenchymal tumors of the gastrointestinal tract. While endoscopic resection techniques have shown to be feasible for removal of GISTs < 3cm, surgical resection is recommended for larger tumors. Neoadjuvant therapy has shown to reduce the size of GISTs allowing complete surgical resection, however its role in endoscopic resection of gastric GISTs has not been established. We describe a patient with multiple comorbidities where the combination of neoadjuvant therapy followed by en bloc resection via submucosal tunnel endoscopic resection (STER) was used for removal of a large gastric GIST.

Case Description:
A 60-year-old female with coronary artery disease, prior abdominal surgery, & obesity presented with abdominal pain. Computed tomography (CT) scan revealed a 4.8 cm mass in the proximal gastric wall partially involving the lesser curvature. Esophagogastroduodenoscopy showed a subepithelial lesion. An endoscopic ultrasound (EUS) examination demonstrated a 4.8 cm lesion in the proximal gastric body. EUS fine needle biopsy confirmed gastric GIST with a mitotic rate of 1/5 without high-risk features. After a multidisciplinary discussion including surgical & medical oncology, a decision was made to pursue neoadjuvant therapy with Imatinib followed by STER due to comorbidities, prior surgery, & tumor location which may increase the need for partial or total gastrectomy if a traditional approach of upfront resection was taken. The patient tolerated neoadjuvant treatment with Imatinib, & repeat CT scan showed a reduced lesion size of 2.2-2.5 cm. The patient proceeded with STER for removal of the gastric GIST (Image 1).

Procedure:
After submucosal injection, a horizontal incision was made to create a submucosal tunnel. Hemostasis was achieved by skeletonizing & cauterizing any visible vessels. Once the tunnel was created, the lesion was dissected off the muscularis propria of the stomach via extension of the incision and accessing the peritoneum via the tunnel. Important landmarks & adjacent organs were identified to prevent injury during dissection (Image 2). The tumor was retrieved from the tunnel through the mucosal entry site. The tunnel was closed using endoscopic suturing. The patient was discharged home after observation. En bloc resection was achieved and histopathologic exam revealed negative deep and lateral margins (R0 resection). There was no recurrence at the 12 & 24 month follow-up.

Conclusions:
This case highlights the potential of using STER combined with neoadjuvant therapy as a minimally invasive, safe, and effective method for en bloc resection of large gastric submucosal lesions. This multidisciplinary approach to removal of gastric GISTs > 2cm resulting in complete endoscopic resection may reduce mortality and morbidity associated with surgery in select patients.