Endocrine Crisis Triggered by Pembrolizumab: A Case of Acute-Onset Diabetes With Diabetic Ketoacidosis

Pembrolizumab is a selective monoclonal antibody targeting the programmed cell death protein 1 (PD-1) receptor. It has transformed the landscape of cancer immunotherapy by enabling the immune system to recognise and destroy malignant cells. Despite its efficacy across a range of malignancies, pembrolizumab's expanding clinical use requires careful consideration of immune-related adverse events (irAEs), including hypopituitarism, adrenocortical dysfunction, thyroid dysfunction, and diabetes mellitus. We report a case of pembrolizumab-induced diabetes mellitus in a previously euglycemic 42-year-old woman treated for stage IIIC melanoma. She developed abrupt-onset, insulin-deficient diabetes presenting as diabetic ketoacidosis, characterized by undetectable C-peptide and negative islet cell autoantibodies, while undergoing adjuvant immunotherapy for stage IIIC melanoma. This report highlights the unpredictable and severe nature of endocrine IRAEs associated with immune checkpoint inhibitors (ICIs), emphasizing the necessity for vigilant monitoring and rapid, multidisciplinary intervention to mitigate morbidity.