MON-105 Atypical Carcinoid of the Thymus Causing Cushing's Syndrome After COVID-19 Infection

Abstract Disclosure: V.M. Rodriguez Edwards: None. V. Fernandez: None. V. Sriganeshan: None. F. Safdie: None. L. Chertman: None. Background: Thymic neuroendocrine tumors (TNETs) account for < 5% of thymic epithelial tumors (TETs). The incidence of carcinoids of the thymus is 0.2 per million people per year, responsible for ∼ 5% of ectopic Cushing’s syndrome cases. TETs are associated with dysfunction of the immune system and reactive thymic hyperplasia has been described following COVID-19 infection. Clinical Case: A 59-year-old female presented with worsening hypertension, hypokalemia and metabolic alkalosis 1 month after she had a mildly symptomatic COVID-19 infection. On physical exam, she had supraclavicular and dorsocervical fat padding, facial rubor, and hirsutism. Cushing’s Syndrome (CS) was suspected. A 1 mg dexamethasone suppression test (DST) with a cortisol level of 99 mcg/dL (n: 4-22 mcg/dL), an 8 mg DST with a cortisol level of 101 mcg/dL and 24-hour urine free cortisol of 4399.2 mcg (n: 4-50 mcg/24h) confirmed hypercortisolism. An ACTH level of 989 pg/ml (n: 6-50 pg/ml) confirmed this was ACTH dependent hypercortisolism. MRI pituitary protocol showed a convex superior margin of the anterior aspect of the pituitary gland that could reflect a microadenoma. She underwent an inferior petrosal sinus sampling, with ratios indicating that ACTH production was not of pituitary origin, but rather ectopic. A CT of the chest, abdomen and pelvis with IV contrast showed an attenuating anterior mediastinal mass of 3.7 x 4.0 x 3.9 cm with heterogenous contrast enhancement and internal areas of hypoattenuation, multiple circumscribed hypodensities in the pancreatic body and a hepatic hemangioma. A PET/CT (Dotatate) showed a 4.5 cm dotatate avid anterior mediastinal mass, with no other uptake in abdomen or pelvis. The anterior mediastinal mass was resected via robotic video-assisted thoracoscopic left upper lobe wedge resection. Histopathology examination revealed an atypical carcinoid tumor within thymic tissue with a Ki-67 index of 40%. Immunohistochemistry stains for AE1/AE3, chromogranin, synaptophysin, INSM1, and ACTH were positive, supporting that this thymic neuroendocrine tumor was the cause of the patient’s CS. Based on these findings, the TNM staging was pT1aN1. The patient’s CS resolved after surgical intervention. Due to lack of treatment guidelines, she was started on adjuvant cisplatin and etoposide using lung neuroendocrine tumor guidelines. Conclusion: This case contributes to the limited literature on ACTH producing carcinoids of the thymus to help build future guidelines. As it was following a COVID-19 infection, it raises the possibility that the inflammatory response triggered by COVID-19 played a role in the exacerbation of an ACTH-secreting thymic carcinoid tumor potentially via leukemia inhibitory factor, a thymic cytokine known to stimulate ACTH release and associated with tumorigenesis. Presentation: Monday, July 14, 2025