SUN-014 A case of Pembrolizumab induced adrenal insufficiency and thyrotoxicosis

Abstract N.M. Rodrigues: None. S. Bodepudi: None. Y. Qin: None. K.H. McKinney: None. Background: Pembrolizumab is a programmed cell death protein 1 inhibitor (PD-1), an immune check point inhibitor used in the treatment of cancers such as Melanoma and Breast cancer. The reported thyroid dysfunctions related to immunotherapy are hypothyroidism and hyperthyroidism which occur in approximately 8% and 3.4% of patients on single agent pembrolizumab, respectively. In contrast, hypophysitis or adrenal insufficiency is reported in fewer than 0.8% of patients on pembrolizumab. Clinical presentation: A 40-year-old African American female was diagnosed with left breast upper inner quadrant clinical prognostic stage IIIB (T3N2bM0) triple-negative invasive ductal carcinoma. She was started on neoadjuvant therapy with 4 cycles of Pembrolizumab, Carboplatin, Paclitaxel, Doxorubicin, and Cyclophosphamide and 4 cycles of Adriamycin, Cyclophosphamide, and Pembrolizumab. Three weeks after completing the treatment, she was admitted to hospital for nausea, vomiting, dizziness and hypotension with BP 60/40 mm Hg. ACTH stimulation test confirmed adrenal insufficiency with baseline am cortisol only <0.2 ug/dL and low ACTH of 2.5 pg/mL. She was started on adrenal replacement which resolved her symptoms and discharged on hydrocortisone. In addition, thyroid dysfunction was also noted with suppressed TSH of <0.02 mIU/L and high Free T4 of 4.34 ng/dL and high Free T3 of 13.4 pg/mL. TSH receptor antibody and TPO antibody were negative, suggestive of thyroiditis. She was treated with propranolol for palpitations. She had normal thyroid function tests before and during the immunotherapy. Conclusion: We reported a rare case of pembrolizumab induced adrenal insufficiency and thyrotoxicosis. It is very uncommon for pembrolizumab to cause adrenal insufficiency coexisting with thyroiditis. Also, these adverse events occurred after she finished 8 cycles of pembrolizumab. Thus, it is important to monitor both thyroid function and adrenal function periodically, not only when they are on pembrolizumab, but also after they have finished the treatment, as timely diagnosis and management of adrenal insufficiency is crucial to prevent adverse outcomes. Sunday, June 2, 2024