Case Presentation: We report the case of a 45-year-old female with stage IA triple-negative breast cancer treated with neoadjuvant chemotherapy and pembrolizumab who developed secondary adrenal insufficiency due to adrenocorticotropic hormone (ACTH) deficiency six months after stopping the immune checkpoint inhibitor. She presented with persistent nausea, vomiting, weight loss, and altered mental status. Laboratory results [...]