SUN-938 Rare Case of Ectopic Cushing Syndrome Caused by ACTH Secreting Thymic Neuroendocrine Tumor in a Patient with Multiple Endocrine Neoplasia Type 1

Introduction Cushing syndrome (CS) represents an uncommon manifestation of MEN1 and can be caused by both ACTH dependent or independent etiologies. Among them, ectopic ACTH secretion from a Thymic neuroendocrine tumor (TNET) in MEN1 is rare, with very few cases reported so far in literature. We report a case of Ectopic Cushing syndrome (ECS) in a MEN1 patient (pt) with multiple tumors, secondary to ACTH-secreting TNET. Case description: A 44 year old male presented to our institution for nausea, vomiting, dizziness. He had initial workup which revealed multiple tumors (papillary thyroid cancer, thymic mass, parathyroid adenomas, bilateral adrenal nodules, macroprolactinoma, peripancreatic nodules). Given concern for MEN 1, genetic testing was performed which was confirmative. Hormonal workup at this time for adrenal nodules was negative including low dose dexamethasone suppression test(DST). The immobile thymic mass was found to be poorly differentiated NET on biopsy with Ki-67 >50% with vascular invasion and adhesions to lung/chest wall on VATS, not amenable to surgery. The pt declined chemotherapy and radiotherapy due to poor social support. Six months later, he presented with complaints of shortness of breath, proximal muscle weakness, anasarca. Evaluation revealed AM cortisol >60 ug/dL(range 6.7-22), high-dose DST Cortisol >60 ug/dL, 24hr urine free cortisol: 8511mcg (range 4-50) and ACTH level: 278pg/mL(range 6-50) confirming ACTH-dependent CS. Special stains from the previous TNET biopsy demonstrated positive staining for ACTH confirming ectopic ACTH secretion. Ketoconazole and chemotherapy with Etoposide and Carboplatin was started, however he clinically deteriorated and expired a few weeks after diagnosed of ECS. Discussion: TNET in MEN 1 is rare, with a prevalence of 3-8%. TNET are unusual neoplasms that account for 2% to 7% of all mediastinal tumors. TNET in MEN1 rarely secrete functional hormones with very few reported Ectopic ACTH secretion. MEN1 associated ECS from TNET is an aggressive disease with local invasion of adjacent mediastinal structures or metastasis being common, resulting in poor prognosis as demonstrated in few case reports including our case. Radical surgery of involved adjacent structures and adjuvant local RT can provide local disease control. Conclusion: Our pt is a rare case of ECS from TNET in MEN1 with poor prognosis. A special feature of this case is that the patient had initial negative evaluation for hypercortisolemia, however 6 months later he presented with signs and symptoms of severe hypercortisolism, with evaluation confirming transformation into ACTH producing TNET. This conversion is very rarely found in literature and adds to the unique presentation of the case.