FRI508 A Case Of Durvalumab Induced Hypothyroidism

Disclosure: E.D. Cecilio La Riva: None. C. Acosta: None. A.J. Manzano: None. Background: Immune checkpoint inhibitors (ICIs), like Durvalumab, have become a mainstay in cancer treatment as they have significantly improved survival rates, especially for lung cancer. These treatments, however, have been associated with immune-related adverse events (irAEs) including dermatological manifestations, gastrointestinal symptoms, and endocrinopathies. Clinical Case: A 62-year-old male was diagnosed with a poorly differentiated adenocarcinoma with signet ring cell features stage IIIA of the right upper lobe with concurrent prostate cancer who was initially started on chemotherapy with Cisplatin/Pemetrexed for two months (four cycles) and radiation. He was subsequently started on Durvalumab. Thyroid function tests were performed after starting Durvalumab and TSH was 3.46 mlU/L (reference range: 0.40-4.50), Free T4 was 1.2 ng/dL (reference range: 0.8-1.8) and Free T3 was mildly elevated at 4.3 pg/mL (reference range: 2.3-4.2). The patient remained asymptomatic until about 12 weeks later when he began feeling occasional episodes of anxiety and shortness of breath with fatigue that was brought on at random instances. Thyroid function tests at that time showed an undetectable TSH at <0.01, an elevated free T3 at 4.9, and a normal free T4 at 1.6. Immunotherapy was continued and the patient was referred to endocrinology. Repeat thyroid function tests 8 weeks later showed an elevated TSH at 19.55, decreased free T4 at 0.7, and a normal free T3 at 3.1. The patient was started on levothyroxine at that time with improvement of his symptoms. Upon follow-up 4 weeks later, TSH was found at 30.56 and free T4 at 0.9 which improved with levothyroxine dose adjustment. Conclusion: The case of a patient with thyroiditis beginning as transient hyperthyroidism on Durvalumab is described. Hypothyroidism occurs in about 1.82% of patients on ICIs, with more common occurrences on Nivolumab (51.38%) and Pembrolizumab (24.44%). The incidence of hypothyroidism and thyroiditis on Durvalumab is about 3.11% and 2.04% respectively. Thyroid dysfunction with ICIs occurs with PD-1/PD-L1 blockade and an inflammatory, destructive thyroiditis can be seen. Routine monitoring of thyroid function should be performed before and throughout treatment with an ICIs. Preexisting autoimmune thyroid disease may be a risk factor for developing thyroid disease during treatment, but this has not been well studied. Meta-analysis has shown that preexisting autoimmune disease was a risk factor for irAE incidence. This case highlights the importance of proactive monitoring of thyroid function during treatment. Presentation: Friday, June 16, 2023