7209 Immune Check Point Inhibitors And Periodic Thyroid Function Assessment

Abstract Disclosure: A. Farooqi: None. S. Dewan: None. J.Y. Jun: None. S. Farooqi: None. Introduction: Immune checkpoint inhibitors, namely anti-cytotoxic T-lymphocyte-associated antigen 4 (anti-CTLA-4), anti-programmed death 1 (anti-PD-1) and anti-programmed death-ligand 1 (anti-PD-L1) monoclonal antibodies, have emerged in the last decade as a novel form of cancer treatment, promoting increased survival in patients. As they modify the immune system and destroy the immune cells, an array of immune related adverse effects has been noticed, with strong predilection to endocrine organs. Among endocrinopathies, thyroid dysfunction occurs frequently ∼5% especially with the use of anti-PD-L1. While the majority have been cases with destructive thyroiditis leading to transient thyrotoxic phase often followed by transient or permanent hypothyroid phase, the occurrence of hyperthyroidism or Basedow’s disease after the administration of anti CTLA-4 has also been reported. Case Presentation: We present a case of 66-year-old male with past medical history of ischemic cardiomyopathy, atrial fibrillation and metastatic cholangiocarcinoma diagnosed in August 2023. He was initially treated with combined chemotherapy and immunotherapy with duravulamab, anti PD-L1., and then later with duravulamab alone. Three weeks after the second cycle of duravulamab, he was admitted due to episodes of ventricular tachycardia with shock administered through his implantable cardioverter defibrillator. Further evaluation revealed thyroid stimulating hormone (TSH) of <0.01 (0.49-4.67 uIU/L), free T4 of 4.39 (0.61-1.60 ng/dL), total T3 of 160 [87-178 ng/dL], negative thyroid stimulating immunoglobulin and TSH receptor antibody. Of note, three months prior to immunotherapy, TSH was 6.52 uIU/L with normal free T4, pointing to subclinical hypothyroidism. Ultrasound of thyroid revealed enlarged heterogeneous thyroid gland related to thyroiditis. Prednisone 20 mg twice a day was prescribed for presumptive diagnosis of immunotherapy-induced thyroiditis. Patient continued prednisone for 14 days (about 2 weeks) until he ran out. Repeat TSH < 0.01 uIU/L and free T4 5.51 ng/dL with total T3 266 ng/dL confirming ongoing thyrotoxicosis and prednisone was further extended for 2-week period. Conclusion: Thyroid dysfunction is frequently observed during treatment with immune check point inhibitors. While increased body weight and elevated inflammatory markers at baseline are associated with development of thyroid dysfunction, there is no definite predictor identified. This case highlights the importance of periodic assessment of thyroid function test to identify and manage thyroid dysfunction in a timely fashion to avoid potential development of life-threatening consequences of thyroid dysfunction including thyroid storm. Presentation: 6/3/2024