Pembrolizumab and diabetes: a case of diabetic ketoacidosis in a patient with metastatic melanoma

Introduction The advent of immunotherapy has revolutionised the management of certain malignancies, and its use has increased over the past decade. Monoclonal antibody therapies known as checkpoint inhibitors work by enhancing the immune response against malignant cells by blocking the pathways that inhibit T-cell regulation. Checkpoint inhibitors can be administered alone or in combination as an intravenous infusion every 3-6 weeks for a maximum of two years. However, about 10% of patients may experience endocrine adverse effects. Thyroid disease and hypophysitis are those most commonly encountered; there are also reports of diabetes mellitus and primary adrenal insufficiency as well as rarer endocrinopathies. Pembrolizumab, an immune checkpoint inhibitor, received FDA approval in 2014 for advanced melanoma, and in 2015 for metastatic non-small cell lung cancer. It is also approved for recurrent/metastatic head and neck cancer, and for refractory classical Hodgkin’s lymphoma. We report the case of a 75-year-old man who developed new-onset diabetes mellitus and diabetic ketoacidosis while undergoing pembrolizumab chemotherapy for metastatic melanoma. He was not taking steroids.