Pembrolizumab-Induced Immune-Mediated Hepatitis and Concurrent Hepatitis B Reactivation in a Patient With Non-Small Cell Lung Cancer

New immuno-therapeutic agents like pembrolizumab used in cancer treatment are known to cause immune-mediated hepatitis. Most of these cases are straightforward when the onset of transaminitis correlates with the introduction of the medication. This agent causing hepatitis B reactivation has been reported only once. To have both these adverse effects occurring at the same time in a patient is uncommon and presents a clinical challenge. Our patient was a 49-year-old gentleman diagnosed with metastatic adenocarcinoma of the lung seven months ago. He was started on pembrolizumab, as the malignant tissue obtained during biopsy had high program death-ligand 1 (PDL1) expression. On reviewing the labs ordered during the time of cancer diagnosis, this man has evidence of chronic hepatitis B with positive hepatitis B surface antigen and positive hepatitis B core immunoglobulin G (IgG) antibody. He presented with acute hepatitis, and workup showed features of hepatitis B reactivation, but the extent of reactivation was not adequate to explain the presentation, hence investigations were pursued. This led the way to the diagnosis of a combined hepatitis B reactivation and drug-induced immune hepatitis in this case. He responded promptly to the withdrawal of the agent and steroids. On follow-up, his liver function panel had significantly improved.  This case is very unique in two aspects. First, to our knowledge, there is only one case reported of pembrolizumab-induced hepatitis B reactivation. In addition, our patient also had immune-mediated hepatitis induced by pembrolizumab. It is very rare to have a combination of these two presentations to be seen in a patient at the same time. Pembrolizumab-induced immune hepatitis can coexist with hepatitis B reactivation following therapy with this agent.