Silent Aggressor: Unveiling Large-Cell Duodenal Neuroendocrine Carcinoma.

Duodenal neuroendocrine neoplasms (D-NENs) are uncommon tumors that account for a fraction of duodenal tumors. Although often incidentally discovered, those in the ampullary or peri-ampullary regions may present with symptoms due to biliary or gastrointestinal obstruction, including obstruction or bleeding. We describe a 65-year-old male who presented with fatigue, altered mentation, and melena. His evaluation was notable for severe anemia, metabolic derangements, and laboratory findings with concern for tumor lysis syndrome. Emergent management with hemodialysis and supportive care stabilized his condition. Esophagogastroduodenoscopy revealed a Forrest class 1B duodenal ulcer and histopathological examination of obtained biopsies confirmed a diagnosis of large-cell neuroendocrine carcinoma with a Ki-67 index of approximately 80%. Subsequent imaging demonstrated extensive hepatic involvement. Given the advanced stage of the disease and after multidisciplinary discussion, the patient elected against further oncologic intervention. This case highlights the diagnostic challenges and aggressive nature of high-grade D-NENs, emphasizing the importance of early recognition and a multidisciplinary treatment approach.