Type 1 diabetes mellitus affected by potential toxicity from long-term use of nivolumab.

We present a case of type 1 diabetes mellitus (T1DM) that developed in a 53-year-old man after long-term treatment with nivolumab. The patient underwent total gastrectomy for gastric cancer at 40 years of age, and he was started on nivolumab at age 48 years for treatment of a recurrent lesion that proved resistant to standard chemotherapy. Nivolumab treatment resulted in complete response, but, after the 136th infusion of the drug at age 53 years, the patient was hospitalized for sudden onset of diabetic ketoacidosis. He was diagnosed with immune checkpoint inhibitor-induced T1DM (ICI-DM), which developed 1988 days (284 weeks) after initiation of nivolumab. HLA typing revealed disease susceptibility alleles for both fulminant T1DM and ICI-DM. With the increased survival after the ICI treatment, delayed-onset irAEs after long-term use of ICI have been reported; however, delayed-onset ICI-DM remains to be elucidated. This case provides important insight into ICI-DM that develops after prolonged ICI administration, and it suggests that patients should be monitored for ICI-DM regardless of the duration of ICI therapy.