Immune checkpoint inhibitor‐induced diabetes mellitus (CPI‐DM) is a rare but significant side effect of treatment with immune checkpoint inhibitors. It can cause severe hyperglycemia which can lead to diabetic ketoacidosis (DKA) or hyperglycemic hyperosmolar state (HHS). These two critical diseases can cause mortality. We reported a 62-year-old man with sudden onset of hyperglycemia after he accepted chemotherapy with Cetuximab+Nivolumab.

This 62-year-old man had been diagnosed soft and hard palate squamous cell carcinoma, cT4bN2cM0, stage IVb on October 17, 2023. He started treatment with Cetuximab and Nivolumab on August 05, 2024. Severe hyperglycemia (662 mg/dL) was noted on October 16, 2024. He denied any history of diabetes mellitus. We started to survey the reasons of the hyperglycemia.

We surveyed the reasons of the hyperglycemia and excluded infection, DKA, HHS, pancreatic diabetes, hyperthyroidism and Cushing syndrome. Because glucagon stimulation test showed positive result, CPI-DM was suspected.

TOUJEO and Insulin Aspart as basal and bolus insulin therapy were given to the patient. There was no severe hyperglycemia, DKA or HHS found at follow-up. Because the patients' beta-cell function is usually and permanently compromised, so patients required lifelong insulin therapy and follow-up.