S6350 Synchronous Diffuse Large B-Cell Lymphoma and Gastric Adenocarcinoma: A Rare Dual Malignancy Presenting With Gastric Outlet Obstruction and Fistulous Complication

Introduction: Concurrent presentation of 2 primary gastrointestinal (GI) cancers is extremely rare, with limited cases reported in the literature. Primary gastrointestinal lymphoma comprises less than 5% of GI malignancies, while gastric adenocarcinoma remains 1 of the most prevalent GI cancers globally. The synchronous occurrence of diffuse large B-cell lymphoma (DLBCL) and gastric adenocarcinoma presents unique diagnostic and therapeutic challenges. This case highlights a rare instance of concurrent dual GI malignancies complicated by obstruction and fistulization, requiring complex multidisciplinary management. Case Description/Methods: A 69-year-old man with a past medical history of inguinal hernia repair presented with 1 week of intractable nausea and vomiting. Two months earlier, he had reported abdominal discomfort, distention, anorexia, and a 15-pound weight loss over 4 weeks. Computed tomography (CT) imaging showed mural thickening of the duodenum, colonic thickening, and a fistula between the duodenum and ascending colon. Esophagogastroduodenoscopy (EGD) revealed a 4 cm cratered gastric ulcer and a large fungating duodenal mass. Biopsies confirmed T3N2 poorly differentiated gastric adenocarcinoma with signet ring cells and DLBCL involving the duodenum with colonic fistula. On admission, he was afebrile and hemodynamically stable, with mild abdominal tenderness. Laboratory studies showed leukocytosis, anemia, and elevated alkaline phosphatase. A port was placed, and R-CHOP chemotherapy was initiated for lymphoma. He developed bilateral segmental pulmonary emboli requiring anticoagulation. Shortly thereafter, he acutely decompensated with respiratory failure and was found to have a bowel perforation. He underwent emergent surgery, including right colectomy, partial Whipple, and gastrectomy. His course was complicated by ongoing sepsis, transfusion requirements, and multiorgan failure. Despite further surgical interventions, he remained critically ill and passed away. Discussion: Synchronous primary gastrointestinal malignancies are exceedingly rare and require highly individualized treatment strategies. The initial plan to treat lymphoma first with chemotherapy was derailed by perforation, necessitating emergent surgery. This illustrates the challenges in managing coexisting cancers, where treatment of one malignancy may exacerbate complications of the other. Given the rarity of such presentations, additional case reports are essential to guide management strategies and inform clinical decision-making in similarly complex scenarios.