Ectopic Adrenocorticotropic Hormone Production in a Stage IV Neuroendocrine Tumor: A Rare Presentation of Cushing's Syndrome.

Neuroendocrine tumors (NETs) are heterogeneous neoplasms that arise from neuroendocrine cells, resulting in endocrine imbalances that impact quality of life and prognosis. Ectopic adrenocorticotropic hormone (ACTH) production by NETs is a rare cause of ACTH-dependent Cushing's syndrome. While the majority of these cases are associated with intrathoracic tumors, recent reports have indicated an increasing incidence of cases originating from diverse anatomical sites. Furthermore, despite comprehensive imaging efforts, a substantial proportion of cases remain challenging to localize. In this case, we describe a 54-year-old man with a stage IV NET with metastatic liver and pancreatic lesions, who presented with Cushing's syndrome due to ectopic ACTH production. The patient exhibited symptoms of severe hypercortisolism, including weight gain, proximal muscle weakness, acute-onset heart failure, and hypertension. Imaging revealed bilateral adrenal hypertrophy. Laboratory tests revealed hypokalemia and hyperglycemia and confirmed elevated cortisol levels and a lack of suppression after dexamethasone administration, consistent with ectopic rather than pituitary ACTH production. The patient was treated with metyrapone because ketoconazole was contraindicated because of liver metastasis and recent upper gastrointestinal bleeding requiring proton pump inhibitor use. This case highlights the rare occurrence of ACTH-producing NETs and emphasizes the importance of considering this diagnosis in cases with similar presentations. Furthermore, medical management of this patient without surgical intervention, owing to multiple contraindications, offers an important perspective for treating complex cases.