Pembrolizumab: a case of drug‐induced autoimmune diabetes mellitus and colitis

Abstract Background Immunosuppressive molecules such as cytotoxic T lymphocyte‐associated antigen 4 ( CTLA ‐4), programmed cell death protein ( PD ‐1) and its ligand ( PD ‐L1) are markedly overexpressed in the tumour microenvironment, providing a means for immune escape. Targeting these molecules, novel immunotherapies manipulate the host immune system to better detect and kill cancer cells. This paper describes a case of drug‐induced autoimmune colitis and type 1 diabetes mellitus (T1 DM ) attributed to pembrolizumab. Clinical details A 70‐year‐old male presented with a 1‐week history of diarrhoea, vomiting, mucositis and loss of appetite following his third treatment with pembrolizumab infusion for metastatic melanoma. The patient's pathology results and clinical symptoms were consistent with a diagnosis of colitis and diabetic ketoacidosis ( DKA ). Outcomes The patient's symptoms resolved with interventions from the intensive care unit ( ICU ), endocrinology and gastroenterology teams. Due to the severity of the adverse drug reaction, pembrolizumab was ceased. The patient was discharged from the hospital with insulin for his T1 DM and a 1‐month course of weaning prednisolone for his colitis. Conclusion The potential for autoimmune side effects associated with pembrolizumab may not be fully recognised by all clinicians. This case report highlights the potential for serious adverse events and serves to demonstrate the requirement for clinicians to develop a routine approach for early identification and management of these events.