Non-insulin-dependent Diabetes Mellitus Induced by Immune Checkpoint Inhibitor Therapy in an Insulinoma-associated Antigen-2 Autoantibody-positive Patient with Advanced Gastric Cancer

A 70-year-old man with insulinoma-associated antigen-2 autoantibodies developed diabetes mellitus (DM) without ketoacidosis after starting nivolumab to treat advanced gastric cancer. He subsequently exhibited preserved insulin-secretion capacity for over one year. Immune checkpoint inhibitors (ICIs) infrequently cause type 1 DM associated with the rapid loss of insulin secretion and ketoacidosis as an immune-related adverse event. ICIs may also cause non-insulin-dependent DM by inducing insulin resistance if there is islet autoantibody-related latent beta-cell dysfunction. The present case highlights the importance of testing blood glucose levels regularly to diagnose DM in patients treated with ICIs, even if they do not have diabetic ketoacidosis.