New-Onset Autoimmune Diabetes Mellitus Presenting As Diabetic Ketoacidosis in Association With Pembrolizumab Therapy and Long Term Follow-Up: Case Report

Pembrolizumab, an immune checkpoint inhibitor (ICI) that acts against receptor programmed cell death-1 (PD-1), is currently being used in the treatment of a variety of cancers. As PD-1 is also present on other non-malignant tissues, this results in side effects involving a multitude of organ systems termed immune-related adverse effects (irAEs). Programmed cell death-1 is expressed on the beta cells of islets of the pancreas, and their destruction can result in hyperglycemia and the onset of new diabetes mellitus (DM). Thus, the anti-PDI action of pembrolizumab can lead to autoimmune-related DM. We present a case of a 62-year-old male who developed new-onset DM after 12 cycles of pembrolizumab with a severe presentation in the form of diabetic ketoacidosis (DKA) and ICU stay. Our case underscores the importance of physician awareness, frequent lab monitoring and patient education about this rare but potentially fatal irAE of ICI. It also strengthens existing data in literature suggesting the association of irAEs with improved efficacy of ICI therapy.