Is immune checkpoint inhibitor-associated diabetes the same as fulminant type 1 diabetes mellitus?

Pembrolizumab is an anti-cancer drug that targets programmed cell death protein-1 (PD-1) receptors on lymphocytes resulting in their activation against tumour cells. PD-1 receptors are also interspersed in endocrine organs and pembrolizumab use has long been associated with hypophysitis and thyroiditis. Since the introduction of immune checkpoint inhibitors (ICI), several cases of fulminant type 1 diabetes mellitus (FT1DM) have been reported. However, it is unclear if FT1DM and ICI-induced diabetes are the same pathology. We review the existing literature of ICI-induced diabetes to investigate its nature and to what extent it represents type 1A diabetes and/or FT1DM (type 1B diabetes) using an example case. Our review showed that ICI-induced diabetes may be a different entity to FT1DM. Furthermore, there is limited evidence for the management of ICI-induced T1DM. Further research into its pathophysiology will improve management and possibly prevent this burdensome complication. © Royal College of Physicians 2020. All rights reserved.