Pembrolizumab-Induced Hypophysitis With Isolated Adrenocorticotropic Hormone (ACTH) Deficiency: A Rare Immune-Mediated Adverse Event

Pembrolizumab is an immune checkpoint inhibitor that targets the programmed cell death protein 1 antigen to stimulate an immune response against tumor cells. It has successfully induced remission in patients with severe metastatic disease, including those refractory to other chemotherapeutic regimens. Immune checkpoint inhibitors may result in immune-related adverse events affecting multiple organs, including endocrine organs, leading to thyroiditis and hypophysitis, among others. Isolated adrenocorticotropic hormone deficiency and hypophysitis have been reported in patients treated with nivolumab, another programmed cell death protein 1 inhibitor. However, clinical characteristics of these side effects associated with pembrolizumab have yet to be described in detail. We describe a case of an 85-year-old Caucasian male undergoing treatment of metastatic urothelial carcinoma with pembrolizumab, who abruptly developed hypophysitis requiring emergent intervention.