MON-097 Ectopic Cushing Syndrome Secondary to Metastatic Neuroendocrine Tumor of Cecal Origin

Abstract Disclosure: P. Uppal: None. M. Salama: None. F. Fargahi: None. S. Ahmed: None. Background: Ectopic ACTH secretion (EAS) accounts for less than 5% of Cushing’s syndrome. When diagnosed, the primary tumor in the majority of patients is of pulmonary origin, with bronchial neuroendocrine tumors being the most common etiology. EAS from tumors of colonic origin is uncommon and reported to be as low as three cases per one million persons in one year. Case: We describe the case of a 72-year-old man with a history of hypertension, easy bruising, and progressive anasarca who presented to the hospital after a mechanical fall. Laboratory testing showed severe hypokalemia, hypernatremia, metabolic alkalosis, and elevated liver enzymes. The hypokalemia was refractory to potassium supplementation and spironolactone dose titration. A hormonal workup found elevated cortisol, no cortisol suppression on 1mg dexamethasone suppression test, elevated ACTH and increased 24-hour urinary-free cortisol. An 8 mg dexamethasone suppression test failed to suppress cortisol, supporting ACTH-dependent Cushing’s syndrome from an ectopic source. Pituitary imaging did not identify a central source for excessive ACTH secretion. MRI of the abdomen revealed numerous liver lesions, consistent with metastatic disease, which on biopsy were found to be of gastrointestinal (GI) origin. The hospital course was remarkable for lower GI bleeding, altered mentation, and an NSTEMI. A colonoscopy found a large mass in the cecum which was confirmed to be neuroendocrine in origin and the primary source for EAS. Of note, the patient had a negative screening colonoscopy 14 years prior and a negative fecal immunochemical-DNA test 2 years before this hospitalization. He declined chemotherapy and was begun on palliative octreotide. Ketoconazole was not opted for due to transaminitis. He was started on metyrapone prior to being discharged to hospice. Discussion: This case illustrates that Cushing’s syndrome from an ectopic source poses both a diagnostic and treatment dilemma. Cushing’s syndrome due to ectopic ACTH secretion is an endocrinological emergency due to the degree of hypercortisolism. Despite colon cancer being one of the more common malignancies, EAS due to underlying colonic malignancy is very uncommon, and vice-versa, colon cancer does not commonly present as EAS. Beyond surgical cure, ectopic Cushing is treated through steroidogenesis inhibitors. Liver function tests need to be monitored while on ketoconazole and limited availability is a challenge while utilizing metyrapone as a steroidogenesis inhibitor. Presentation: Monday, July 14, 2025