P3.M257: Identification of an EWSR1-BEND2 Fusion-Positive Pediatric Gastric Tumor through RNA Sequencing: A Case Report

Introduction: EWSR1-BEND2 gene fusions have been reported in adult pancreatic neuroendocrine tumors, salivary gland tumors, and pediatric gliomas, but this fusion has not been identified in pediatric gastric tumors. This report aims to describe a rare pediatric gastric tumor, discuss its clinical presentation, histopathology, diagnosis, and treatment, and highlight the importance of further study into the molecular characterization of pediatric tumors.

Case Description: A 15-year-old female presented with shortness of breath and epigastric pain. Abdominal ultrasound, contrast-enhanced computed tomography, and endoscopic ultrasound demonstrated a large solid and cystic mass. Due to mass effect, it was difficult to discern if the mass arose from the pancreas or the stomach. Fine needle aspiration initially supported the diagnosis of solid pseudopapillary neoplasm based on morphology and focal nuclear beta-catenin positivity. The patient subsequently underwent an exploratory laparotomy, at which time the mass was discovered to be arising from the posterior body of the stomach without invasion into surrounding organs. A partial gastrectomy and gastric mass resection were performed.

Discussion: H&E sections demonstrated an epithelioid neoplasm with focal trabecular growth. Immunohistochemical stains were remarkable for cytokeratin positivity, with positive CD56 and focal synaptophysin expression. Initial DNA sequencing revealed a novel ATRX variation of uncertain clinical significance without DAXX alteration. Further molecular characterization was then pursued, with RNA transcriptome sequencing revealing a fusion between EWSR1 exon 7 and BEND2 exon 2.

Conclusion: To our knowledge, this is the first report of an EWSR1-BEND2 gene fusion in a pediatric gastric tumor. Expanding our understanding of pediatric gastrointestinal tumors' genetic and epigenetic profiles could carry significant diagnostic and therapeutic implications.