A Case Report of Pembrolizumab-Induced Allergic Hepatitis.

The immune checkpoint inhibitor pembrolizumab is now considered a first-line treatment for recurrent or metastatic head and neck squamous cell cancer. Pembrolizumab is less toxic than conventional chemotherapy but may result in immune-related adverse events. We report a case in which liver injury occurred just two days after the administration of pembrolizumab plus chemotherapy. A 48-year-old woman achieved a complete response after chemoradiotherapy for cT2N3bM0 squamous cell carcinoma of the oropharynx with multiple lymph node metastases. However, the tumor recurred one year later, and she was started on pembrolizumab plus chemotherapy. On day 3, her alanine aminotransferase and aspartate transaminase concentrations markedly increased. She was initially diagnosed with drug-induced liver injury and all medications were withdrawn. Her liver function recovered within two weeks without intervention. The lymphocyte transformation test was only positive for pembrolizumab. Clinicians should consider pembrolizumab-induced allergic hepatitis as a possible cause of liver injury after excluding liver metastasis and immune-related adverse events.