MON-338 Navigating Metastatic Thyroid Cancer in the Context of Amiodarone Induced Iodine Overload

Abstract Disclosure: M.P. Reyes: None. V. Babu: None. S. Mishra: None. A. Mehta: None. Introduction:Radioactive iodine (RAI) is crucial for managing metastatic papillary thyroid carcinoma (PTC). However, chronic amiodarone therapy, with its high iodine content, can cause iodine overload, limiting RAI’s effectiveness. We present a case of metastatic PTC complicated by excess iodine from prolonged amiodarone use.Clinical Case:A 72-year-old woman with PTC, treated by total thyroidectomy in 2005 (no remnant ablation due to low risk), presented in 2024 with bilateral pulmonary nodules noted on routine imaging. Biopsy confirmed metastatic PTC (thyroglobulin, TTF1, and PAX8 positive). She had chronic atrial fibrillation managed with amiodarone for over a decade, resulting in significant iodine overload. Post-thyroidectomy hypothyroidism was treated with levothyroxine (175 mcg/day), maintaining TSH <0.1 mIU/L due to metastatic disease.Diagnostic RAI imaging was contraindicated by iodine saturation. Management included:1. Discontinuing amiodarone and initiating dofetilide to facilitate iodine clearance.2. Suppressive levothyroxine dosing was maintained to keep TSH levels below 0.1 mIU/L, minimizing stimulation of residual thyroid cancer cells.3. Monitoring urinary iodine and thyroid function during a washout period, with imaging to assess disease stability.4. Considering tyrosine kinase inhibitors if disease progressed while awaiting RAI eligibility.Currently, she remains clinically stable without significant progression, and future RAI eligibility is under reassessment.Clinical Lessons:This case highlights the unique complexities of managing metastatic PTC in the context of iodine excess from chronic amiodarone use. Key clinical lessons include:• Chronic amiodarone-induced iodine overload demands strategic tapering of amiodarone and the use of alternative antiarrhythmics.• Maintaining TSH suppression is critical to limiting tumor growth in metastatic PTC.• Close collaboration among endocrinology, cardiology, and oncology balances arrhythmia control and cancer management.• Tyrosine kinase inhibitors offer a viable bridge therapy when RAI is contraindicated or delayed. • Comorbidities, including the need for glycemic control and cardiovascular stability, underscore the importance of comprehensive, personalized care. Presentation: Monday, July 14, 2025