PSAT342 Hypothyroidism After Use Of Immune Checkpoint Inhibitor Therapy In Patient With Graves’ Disease

Abstract

Abstract Background Immune checkpoint inhibitors (ICIs) are commonly used for many cancers. Thyroid gland involvement is the commonest endocrine toxicity seen with this class of drugs. Most common thyroid dysfunction is thyroiditis followed by hypothyroidism with some cases of recovery. There are rare case reports of Graves’ disease induced by ICIs. However, we report a patient with pre-existing Graves’ disease who developed hypothyroidism after immunotherapy. Clinical Case 66-year-old man with metastatic squamous cell carcinoma of lung was referred to endocrine clinic for suppressed TSH. He was diagnosed with metastatic poorly differentiated lung cancer in September 2018. He received cheamotherapy with carboplatin and paclitaxel from October 2018 to January 2019. He was switched to immune checkpoint inhibitors with programmed cell death protein-1 (PD-1) inhibitor pembrolizumab every 3 weeks from February 2019. ICI therapy was stopped in until July 2019 due to immune mediated hepatitis. He was started on high dose steroids. Lung cancer findings remained stable even after stopping ICIs. Prior to starting ICIs his thyroid functions were consistent with hyperthyroidism. He continued to have suppressed TSH until his 6th cycle of pembrolizumab. TSH was found be significantly elevated prior to his 7th infusion. He was referred to endocrinology for further management. Clinically, patient was asymptomatic except for fatigue. Family history was positive for mother with Graves’ disease. Laboratory results on presentation showed significantly elevated TSH, low thyroxine (T4) and triiodothyronine (T3) consistent with diagnosis of primary hypothyroidism. Thyroid stimulating immunoglobulin (TSI) was positive suggesting autoimmune thyroid disease. Thyroid scan showed decreased 24-hour uptake (0.8%). A diagnosis of immune checkpoint inhibitor (ICI) related hypothyroidism was made. He was started on hormonal replacement with levothyroxine 50 mcg daily. Review of previous thyroid blood tests showed suppressed TSH since October 2016, but he was never treated. Thyroid peroxidase (TPO) antibodies were positive in the past. Thyroid sonogram in December 2016 showed a heterogeneous thyroid with no nodules. A radioactive scan in 1/2017 showed normal 24-hour uptake (12%) with no hot or cold nodules. (Fig 1). Since starting levothyroxine, the dose has been adjusted few times and patient has been doing well. Conclusion This is a unique case of patient with Graves’ disease who was cured because of immune related adverse event from use of immune-checkpoint inhibitor therapy. Presentation: Saturday, June 11, 2022 1:00 p.m. - 3:00 p.m.