Pembrolizumab-Induced Isolated Adrenocorticotropic Hormone (ACTH) Deficiency


Pembrolizumab is a programmed death 1 receptor (PD-1) inhibitor. It is used as immunotherapy in various cancers, including metastatic melanoma, non-small cell lung cancer, and, notably, high-risk triple-negative breast cancer. We discuss a case of a 44-year-old female with a past medical history of triple-negative breast cancer who presented with a chief complaint of poor oral intake and fatigue after her fourth cycle of pembrolizumab therapy. The patient was diagnosed with pembrolizumab-induced isolated secondary adrenal insufficiency (AI) and was treated with corticosteroids with improvement in her symptoms. Secondary AI due to pembrolizumab use is a rare yet potentially life-threatening complication. If initial serum cortisol is borderline low, as observed in our patient, repeated testing within shorter intervals should be considered to optimize patient outcomes.