Immune Checkpoint Inhibitor Induced Diabetes MellitusTreated with Insulin and Metformin: Evolution of DiabetesManagement in the Era of Immunotherapy

Immune checkpoint inhibitors (ICPIs) are a breakthrough therapy in oncology and have been approved by the Food and DrugAdministration for the treatment of several malignancies. ICPIs have been reported to cause immune-mediated damage of isletcells leading to ICPI-induced type 1 diabetes mellitus (T1DM). These reports described patients presenting with severe diabeticketoacidosis (DKA). We present a case of a 69-year-old Caucasian male with type 2 diabetes suffering from non-small cell lungcancer and undergoing treatment with pembrolizumab, an anti-programmed cell death protein-1 antibody, who presented toour emergency department with complaints of nausea, vomiting, polyuria, and polydipsia. He was found to have high anion gapmetabolic acidosis with ketosis and elevated blood glucose levels consistent with DKA. Lab workup was consistent with T1DM.Despite being on a tailored insulin regimen, his blood glucose remained elevated, necessitating the addition of metformin to hisregimen which effectively controlled his blood glucose.