S5358 Diagnostic and Therapeutic Challenges in Gastric Adenocarcinoma: A Case of Missed Detection on Biopsy and PET Imaging Requiring Multimodal Endoscopic Management

Introduction: Gastric adenocarcinoma (GA) diagnosis remains challenging due to nonspecific symptoms and limitations in timely workup. Endoscopic biopsy may be nondiagnostic, and positron emission tomography (PET) scans have variable sensitivity, particularly in signet ring histology. This case required multimodal endoscopic techniques for definitive diagnosis after initial biopsy, and PET failed to confirm GA. Case Description: A 64-year-old woman with recent pancreatitis, pulmonary embolism, and septic thrombophlebitis of the left internal jugular vein presented with progressive early satiety, dark urine, and weight loss. Labs showed cholestatic liver enzyme elevation. CT abdomen revealed biliary dilation, gastric antral thickening, and lymphadenopathy. Magnetic resonance cholangiopancreatography confirmed bile duct thickening and lymphadenopathy. Esophagogastroduodenoscopy (EGD) 1-month prior showed a fungating antral mass, but pathology from biopsies revealed only chronic inflammatory changes. PET scan demonstrated hypermetabolic lymphadenopathy without gastric uptake, raising concern for lymphoma. Due to worsening satiety and concern for gastric outlet obstruction, repeat EGD with endoscopic ultrasound (EUS) was performed, confirming a stenotic antral mass. Given significant narrowing, an uncovered metal stent was placed for symptom relief. EUS-guided fine-needle biopsies (FNB) of the mass and periceliac lymph nodes confirmed poorly differentiated adenocarcinoma with signet ring features and metastatic lymphadenopathy, establishing stage IV GA. The patient later developed obstructive jaundice, requiring biliary decompression via internal/external drains. Endoscopic retrograde cholangiopancreatography was not attempted due to antral stenosis and lack of ampullary access. Given her decline and nutritional compromise, she was not an ideal chemotherapy candidate and ultimately decided to transition her to hospice. Discussion: This case highlights the benefit of EUS-FNB in GA diagnosis after an inconclusive biopsy and high suspicion for malignancy. Endoscopic stenting provided symptom relief for gastric outlet obstruction, while biliary decompression required alternative approaches given anatomic challenges. Up to 10% of gastric cancers are missed at EGD. PET scan sensitivity varies, particularly in signet ring GA, where lower metabolic activity leads to false-negative results. This case underscores the need for repeat tissue sampling when there is a strong suspicion, multimodal endoscopic approaches, and strategic therapeutic decisions in complex GA cases.