Endocrine Abstracts

Pembrolizumab, a programmed cell death protein-1 (PD-1) immune checkpoint inhibitor, has transformed cancer therapy but can lead to immune-related adverse events (IRAEs), including insulin-dependent diabetes mellitus. This report details a case of pembrolizumab-induced diabetes mellitus (PIDM) presenting acutely with diabetic ketoacidosis (DKA). A 42-year-old woman with Stage IIIC melanoma, receiving adjuvant pembrolizumab, presented to the emergency department, with a five-day history of polydipsia, abdominal pain, and breathlessness, three weeks after her last treatment. She was diagnosed with DKA, confirmed by an arterial pH of 7.10, serum ketones of 6 mmol/L, bicarbonate of 9 mmol/L, and blood glucose of 26.2 mmol/L. She had no prior history of diabetes, with an HbA1c increasing from 39 mmol/mol four weeks earlier, to 69 mmol/mol at admission. Investigations showed an undetectable C-peptide level (<7 pmol/L), consistent with beta-cell dysfunction, and negative diabetes-associated autoantibodies. Pembrolizumab was identified as the likely cause. This case highlights the importance of recognizing pembrolizumab-induced diabetes mellitus (PIDM) as a potential cause of acute DKA in patients on immune checkpoint inhibitors. Early diagnosis and management, alongside coordinated care between oncology and endocrinology teams, are essential to optimize outcomes.