SAT-310 The Unexpected Endocrine Disruption: β-hCG-Induced Hyperthyroidism in Metastatic Testicular Cancer

Abstract Disclosure: H. Akbari: None. A. Kang: None. R. Devbhandari: None. R. Jhingan: None. Background: β-human chorionic gonadotropin (β-hCG)-induced hyperthyroidism is a rare paraneoplastic syndrome associated with germ cell tumors, particularly those with choriocarcinoma differentiation. β-hCG shares structural similarity with thyroid-stimulating hormone (TSH) and can activate TSH receptors, leading to excess thyroid hormone production. Hyperthyroidism severity correlates with β-hCG levels and typically resolves with chemotherapy. We present a case of β-hCG-induced hyperthyroidism in metastatic non-seminomatous germ cell tumor (NSGCT), highlighting key diagnostic and management challenges. Case Presentation: A 34-year-old male with metastatic NSGCT, composed of choriocarcinoma, teratoma, and somatic-type malignancy, presented with worsening cough, dyspnea, and hypoxia. One month prior, he underwent a right radical inguinal orchiectomy, with pathology confirming NSGCT. Initial tumor markers included α-fetoprotein (AFP) <1.8 ng/mL (normal: <10 ng/mL), lactate dehydrogenase (LDH) 1091 U/L (normal: 140-280 U/L), and β-hCG 129,928 mIU/mL (normal: <5 mIU/mL).On admission, he was afebrile (36.4°C), with a blood pressure of 110/67 mmHg, heart rate of 120 beats per minute, and oxygen saturation of 84% on room air. Laboratory tests revealed suppressed TSH at 0.02 mcIU/mL (normal: 0.35-5.00 mcIU/mL) and elevated free thyroxine (T4) at 1.98 ng/dL (normal: 0.70-1.80 ng/dL), consistent with β-hCG-induced hyperthyroidism. His β-hCG had risen to 507,927 mIU/mL. Contrast-enhanced computed tomography (CT) of the chest ruled out pulmonary embolism but showed significant disease progression, including enlarging lung nodules, extensive mediastinal and hilar lymphadenopathy, ground-glass opacities, and airway narrowing due to lymph node compression. He had recently initiated chemotherapy with bleomycin, etoposide, and cisplatin (BEP) but developed acute hypoxemic respiratory failure, raising concern for bleomycin-induced lung toxicity versus pneumonia. He was started on broad-spectrum antibiotics and methimazole 10 mg daily for symptomatic hyperthyroidism. Due to concerns about pulmonary toxicity, chemotherapy was modified to etoposide, ifosfamide, and cisplatin (VIP), which he tolerated well. Over the following weeks, β-hCG levels declined with chemotherapy, leading to the resolution of hyperthyroidism. Methimazole was discontinued, and the patient remained euthyroid. Conclusion and Clinical Learning: β-hCG-induced hyperthyroidism is an uncommon but significant condition in metastatic germ cell tumors. While typically transient, symptomatic treatment may be needed in select cases. Early recognition is essential, as chemotherapy effectively resolves thyroid dysfunction. A multidisciplinary approach involving endocrinology and oncology is critical to optimizing care and avoiding unnecessary thyroid-specific treatment. Presentation: Saturday, July 12, 2025