6410 Effects of Immune Check Point Inhibitors on Thyroid Function

Abstract Disclosure: V. Kachroo: None. S.K. Wangnoo: None. M.A. Siddiqui: None. Immune check point inhibitors (ICPIs) are the newest agents for the treatment of malignant tumors, showing promising effects and potential, and has immune related adverse events (IRAEs) as well. IRAEs involve various organs and tissues and also cause thyroid dysfunction. This is a non randomized prospective observational study done at a tertiary referral hospital in patients initiated on ICPIs for the underlying malignancies between March 2022 to September 2023. A total of 35 patients were taken after calculating the sample size using appropriate statistical formula. Thyroid function tests (T3, T4, TSH,) were done monthly for first six months and then every three-monthly till 12 months in patients not on any thyroid medication. In patients already getting treatment for hypothyroidism/hyperthyroidism,TSH was assayed monthly for 3 months, then every 3 months for 12 months. Anti TPO antibody levels were done at baseline and at 12 months in all the individuals. Overt and subclinical hyperthyroidism/ hypothyroidism was defined usinh standard criteria.The assay used for the determination of TSH, FT4, FT3 and anti-TPO Antibody was Chemiluminescent Immunoassay (CLIA). Normal reference ranges for TSH was 0.27-4.20 mU/ml, FT4 was 0.90-1.70 ng/dl and FT3 was 2.0- 4.4 pg/ml. Out of 35 patients, 24(68.5%) were males and 11 were females (31.4%). 25.71% already had history of thyroid dysfunction in the form of primary hypothyroidism and were on levothyroxine and no one had hyperthyroidism when they were initiated on ICPIs. Out of 9 patients, 6 patients had no change in dose (66.67%); 2 patients had increased dose requirement (22.22%) and 1 patient had decreased dose requirement (11.11%). Out of remaining 26 patients who didn’t have any thyroid function, 12(46.15%) had new onset thyroid dysfunction. All 26 had hypothyroidism (either overt or subclinical). Out of these 26 patients, 9(34.62%) had overt hypothyroidism and started on levothyroxine as per their age and body weight requirements, 3(11.54%) patients had subclinical hypothyroidism. Out of 12 patients, who developed new onset TDF after initiation of ICPIs, 2 patients became TPO positive and 10 patients had negative TPO Antibodies at the end of 12 months. Kaplan Meir analysis showed that thyroid dysfunction at the end of 3 months was in 13.33% of patients, in 53.85% each at the end of 6 months and 12 months. The mean time of onset of thyroid dysfunction was 3.083 months in (IQR=2.25-3.917 months; 95% CI; SE=0.379). We conclude that thyroid dysfunction in the form of new onset hypothyroidism (subclinical or overt) or increased thyroxine dose requirement in the patient who are already hypothyroid is seen in patients receiving ICPIs. Regular surveillance of thyroid function is warranted in patients receiving these drugs. Presentation: 6/3/2024