SAT-590 Ectopic Cushing’s Syndrome Stemming from Metastatic Medullary Thyroid Cancer

Abstract M. Rachamallu: None. K.M. Tuna: None. J. Haddad: None. S. Habib: None. M. Leon: None. D. Barb: None. Background: Ectopic Cushing’s syndrome is an uncommon manifestation of medullary thyroid cancer (MTC), occurring in less than 1% of diagnosed MTC cases. Typically marked by Cushingoid features, elevated blood pressure, hypokalemia, and hyperglycemia, its primary treatment involves medical management. Bilateral adrenalectomy is considered for refractory cases. Case Presentation: A 41-year-old male with a history of tobacco use, uncontrolled hypertension, and anxiety presented with a progressively enlarging right neck mass over two years. Symptoms included fatigue, weight gain, shortness of breath, purple abdominal striae, erectile dysfunction, and leg swelling. Despite recent initiation of antihypertensive treatments, blood pressure was uncontrolled (181/137mmHg). Physical examination revealed anasarca, a dorsal cervical fat pad, and a large subcutaneous neck mass. Additional findings include a systolic ejection murmur, decreased breath sounds on the right lung base, and edema with purple striate on bilateral flanks. Initial lab workup showed impaired fasting glucose, severe hypokalemia and metabolic alkalosis. Neck imaging revealed an asymmetrically enlarged thyroid with a 4.7 cm right thyroid nodule, and a 5.8 cm level III lymph node. Full-body imaging with CT scan identified mediastinal lymph nodes and a right pleural effusion while normal renal and adrenal findings. A core biopsy of the thyroid mass made the diagnosis of MTC with positive staining for calcitonin and chromogranin. Endocrine workup was obtained to investigate resistant hypertension along with newly diagnosed MTC. It showed significantly elevated cortisol 43.1mcg/dl and 67.0 mcg/dl (7.0-23.0 mcg/dl) with high ACTH 283 pg/ml (normal range 7.2-63.5 pg/ml), suppressed aldosterone of 3.1ng/dl, renin of 0.4 ng/ml/hr and significantly elevated 24 h urine free cortisol 13,899 mcg/24hr (normal range 4-50 mcg/24h) confirming ACTH-dependent ectopic Cushing’s syndrome. Also, highly elevated Calcitonin 32,313.0 pg/ml (normal range 0-7.5pg/ml), CEA 1,498.7ng/ml (normal range 0-3ng/ml) were noted and concerning for metastatic MTC. Additional imaging reveled T11 and T12 pathological compression fractures and biopsy confirmed bone metastasis. After electrolytes replaced adequately, the patient was started on spironolactone, ketoconazole, and Metyrapone for the treatment of hypercortisolism. The patient was referred to a tertiary cancer center for individualized chemotherapy and was initiated on Selpercatinib (positive RET mutation). Conclusion: Ectopic Cushing’s syndrome from MTC poses diagnostic and therapeutic challenges. This case emphasizes the need for a multidisciplinary approach to diagnose and manage metastatic medullary carcinoma with ectopic Cushing’s syndrome, highlighting the complex nature of this disease and the importance of a comprehensive treatment strategy. Saturday, June 1, 2024