Atezolizumab-induced type 1 diabetes mellitus in a patient with metastatic renal cell carcinoma.

Checkpoint inhibitor immunotherapy has revolutionised cancer treatment since its inception. During an inflammatory response, activated cytotoxic T cells expressing programmed cell death protein 1 (PD-1) interact with programmed cell death-ligand 1 (PD-L1) on peripheral tissues to thwart an autoimmune reaction. Cancer cells upregulate PD-L1 expression to evade the immune system and are vulnerable to attack in the presence of PD-1 or PD-L1 checkpoint inhibitors. However, blockade of this pathway also contributes to the unintended side effect of autoimmune endocrinopathies. Atezolizumab, a checkpoint inhibitor against PD-L1, is associated with the rare complication of type 1 diabetes. We present a case of glutamic acid decarboxylase antibody-positive type 1 diabetes developing in a patient with a long-standing history of well-controlled type 2 diabetes following treatment with atezolizumab for metastatic renal cell carcinoma.