Dual Primary Gastric Adenocarcinoma and Diffuse Large B-Cell Lymphoma: A Unique Case With a Cascade of Rare Complications

Concurrent presentation of two primary gastrointestinal cancers is extremely rare. We describe an unusual presentation of a 69-year-old patient without a significant past medical history, who was diagnosed simultaneously with diffuse large B-cell lymphoma and gastric adenocarcinoma. This case is distinguished by the development of severe, rarely reported complications such as duodenocolonic fistula, bowel perforation, pulmonary embolism, and multi-organ failure. The combination of those complications underscores the exceptional complexity of management.