MON-099 Severe Cyclic Cushing Syndrome Due to Ectopic ACTH Secretion by Appendiceal Carcinoid

Abstract Disclosure: R. Desai: None. F. Sidra: None. S. Mirfakhraee: None. J. Liwei: None. P. Polanco: None. S. Al Mutar: None. O. Hamidi: None. Background: Cyclic Cushing syndrome (CS) secondary to ectopic adrenocorticotrophic hormone (ACTH) from an appendiceal carcinoid is extremely rare with only a few published cases thus far. This is the first reported case of a patient with extensive metastatic disease on initial presentation. Clinical Case: A 24-year-old woman with no past medical history was referred to endocrinology after developing 60lb weight gain, acne, fatigue, heat intolerance, lower extremity swelling, palpitations, and anxiety over a 3-month period with secondary amenorrhea 6 months prior to presentation. Family history was significant for bronchial carcinoid in her mother. Physical exam was notable for moon facies, wide purple striae on abdomen, hirsutism, dorsocervical and supraclavicular fat pads. Laboratory workup showed hypokalemia (3.2 mmol/L, n = 3.5-5.3), elevated urine free cortisol (UFC) (473 mcg/24hours, n<50), normal ACTH (16 pg/mL, n = 6-50), normal AM Cortisol level (15.3 mcg/dL, n=5-22) and abnormal 1-mg dexamethasone suppression with cortisol 8.8 mcg/dL (n≤1.8). Repeat UFC two weeks later was still elevated (539 mcg/24 hours). Evaluation with CT abdomen and pelvis revealed a 3 cm enhancing appendiceal mass, enlarged periappendiceal mesenteric lymph nodes, and a 4 cm enhancing right hepatic lobe lesion. Further imaging with Ga-68 Dotatate PET/CT confirmed increased radiotracer uptake in the appendiceal mass, lymph nodes, hepatic mass, and right breast. The patient underwent liver biopsy and pathology showed well different neuroendocrine tumor (NET) grade 1 and positive ACTH stain. Genetic testing was negative. She was unable to tolerate ketoconazole and was initially treated with lanreotide 120mg every 4 weeks. Repeat biochemical testing one month after initiation of lanreotide showed elevated UFC (65mcg/24hrs), elevated ACTH (52 pg/mL) and elevated serum cortisol (36.2mcg/dL). Two weeks later ACTH decreased to 14 pg/mL and serum cortisol was <1 mcg/dL which was concerning for severe cyclic ectopic CS secondary to metastatic NET. She was managed with early bilateral adrenalectomy given severe cyclic CS with extensive tumor burden in a young female hoping to preserve fertility. The pathology of her right adrenal gland was notable for metastatic well differentiated neuroendocrine carcinoma. She was subsequently started on physiologic steroids and underwent extensive debulking surgery. 1.5 years later she had progression of disease requiring initiation of peptide receptor radionuclide therapy (PRRT) but has since been in remission. Conclusion: This case demonstrates the importance of individualized medical management of patients with ectopic ACTH syndrome and highlights the need for consideration of early bilateral adrenalectomy for patients with severe CS and metastatic disease. Presentation: Monday, July 14, 2025