ODP303 Cushing's Syndrome Due to Ectopic Adrenocorticotropic Hormone-Secreting Metastatic Neuroendocrine Tumor

INTRODUCTION: Cushing's syndrome (CS) due to ectopic ACTH secretion (EAS), is an infrequent form of ACTH-dependent CS. EAS results from unregulated ACTH secretion by neuroendocrine tumors (NETs) of various locations resulting in severe hypercortisolism. The progression of CS is usually precipitous. To improve outcomes, it is imperative to recognize early so that treatments of cortisol-induced comorbidities and targeted treatments can be initiated. CASE PRESENTATION: A 74-year-old female presented to an outside hospital with fatigue, bilateral lower extremity edema and intractable hypokalemia. She was later transferred to our facility, where workup of CS was initiated. She underwent a 1mgdexamethasone suppression test (DST)which resulted in an unsuppressed 8amcortisol of 34.7 ug/dL (<2 ug/dL). This was followed by a 4mgDST, again resulting in an unsuppressed 8amcortisol of25.4 ug/dL. A 24-hour urine cortisol level was collected and resulted at 2,108.9 ug/d (<45 ug/d). ACTH level was elevated at 136 pg/ml (7.2-63.3 pg/ml). CT abdomen/pelvis identified liver lesions concerning for metastatic disease. PET DOTATATE revealed multiple liver lesions and a few pulmonary nodules. Biopsy of liver lesions demonstrated strongly positive staining of synaptophysin and chromogranin confirming NET, with a weak TTF-1 positivity suggestive of pulmonary origin. Lanreotide injections were initiated for tumor control and ketoconazole for treatment of persistent hypercortisolism. Despite titration of ketoconazole, symptoms and labs showed minimal improvement. Osilodrostat was then added as a third line and examethasone was initiated in a block and replace approach. The regimen of lanreotide, osilodrostat and ketoconazole improved her24-hoururine cortisol to 15 from 2,109 ug/24hr. Subsequently patient underwent trans-arterial chemoembolization (TACE) of the liver lesions with resolution of hypercortisolism. She is currently only on Lanreotide for tumor control. DISCUSSION: NET with ectopic ACTH production is rare. While primary tumor location was not definitively identified, multiple lung lesions and histopathology suggested primary lung tumor with hepatic metastases. 20-40% of all NETS originate in the chest. Patient management necessitates a multidisciplinary approach not only for the diagnosis and treatment of CS but also for the specific management of neuroendocrine tumors (NET). This case highlights a rare presentation of EAS, and aggressive treatment modalities needed to treat symptoms of excess cortisol production and tumor progression. Presentation: No date and time listed