Detailed Time Course of Decline in Serum C-Peptide Levels in Anti–Programmed Cell Death-1 Therapy–Induced Fulminant Type 1 Diabetes

Fulminant type 1 diabetes (FT1D) is a novel subtype of type 1 diabetes (T1D) and is characterized by a relatively low glycated hemoglobin (HbA1c) level at onset, despite the abrupt occurrence of marked hyperglycemia with ketosis or ketoacidosis (1). Recent studies have shown that anti–programmed cell death (PD)-1/anti–PD-ligand 1 (PD-L1) therapy for malignancies leads to the development of T1D including FT1D (2–4). In typical FT1D, insulin secretion capacity is completely exhausted within ∼7 days after the onset (1); in some cases, a rapid loss of insulin secretion was observed during 2 days prior to onset of diabetic ketoacidosis (DKA) (5). Meanwhile, the detailed time course of insulin secretion capacity in anti–PD-1 therapy–induced FT1D has not yet been reported. We present a case of an 82-year-old Japanese man with squamous cell cancer of the lung, who had received multiple courses of anti–PD-1 immunotherapy (pembrolizumab) every 3 weeks for ∼12 months. Written informed consent was obtained from the participant. On the day of the 16th course of anti–PD-1 therapy, his casual plasma glucose and HbA1c levels were 106 mg/dL and 5.8% (40 mmol/mol), respectively. However, a blood test performed on the scheduled day of the 17th course revealed his casual plasma glucose was 432 mg/dL; thus, he was immediately hospitalized without …