Atezolizumab-induced fulminant type 1 diabetes mellitus occurring four months after treatment cessation.

Atezolizumab is an immune checkpoint inhibitor (ICI) that is often associated with the development of several immune-related adverse events, including fulminant type 1 diabetes mellitus (F1DM). Here, we present the case of a 73-year-old woman who was diagnosed with lung adenocarcinoma after surgical lung lobectomy. Two years later, she developed pulmonary metastasis, and atezolizumab treatment was initiated after seven years. However, she only completed two cycles of atezolizumab treatment because of disease progression. Four months after the interruption of atezolizumab treatment, she presented to the emergency department with fatigue and vomiting. On admission, she had a serum glucose level of 962 mg/dL, metabolic acidosis, and elevated ketone body levels. She was diagnosed with diabetic ketoacidosis induced by atezolizumab treatment. Her symptoms improved by insulin therapy. When ICIs are administered, care should be taken regarding the development of F1DM.