New onset autoimmune diabetes mellitus and hypothyroidism secondary to pembrolizumab in a patient with metastatic lung cancer.

Programmed cell death 1 (PD1) inhibitors such as pembrolizumab can cause endocrine immune-related adverse events (irAE), including thyroid dysfunction and type 1 diabetes mellitus (T1DM). Thyroid dysfunction is the most frequent endocrine irAE secondary to PD1 inhibitors. Autoimmune diabetes and possible resultant diabetic ketoacidosis are rare, but life-threatening adverse events associated with pembrolizumab. Pembrolizumab-induced T1DM often present with relatively low HbAlc levels, reflecting the fulminant onset of β-cell destruction. Patients treated with pembrolizumab and other immune checkpoints inhibitors should be monitored regularly for hyperglycaemia and thyroid dysfunction.