Pembrolizumab-Induced Delayed-Onset Hepatitis.

Hepatitis is one of the serious immune-related adverse events (irAEs). However, delayed-onset hepatitis induced by immune-checkpoint inhibitors (ICIs) is rare, and the histopathological features remain to be clarified. A 65-year-old woman with advanced lung adenocarcinoma in the right upper lobe (cT4N3M1c, c-stage IVB) received four courses of pembrolizumab. Her hepatic and biliary tract enzyme levels started increasing 2 months after the final administration of pembrolizumab, and the elevated levels of these enzymes prolonged. Liver biopsy revealed panlobular infiltration of inflammatory cells, and most of the infiltrating inflammatory cells were lymphocytes; however, there were a small number of neutrophils, eosinophils, and plasma cells. There was no confluent necrosis. Furthermore, immunohistochemical analyses proved that infiltrating lymphocytes were predominantly CD3-positive (CD3+) and CD8+, and few CD20+ and CD4+ lymphocytes were observed. Based on these findings, she was diagnosed with a case of hepatitis as an irAE. Administration of prednisolone (0.5 mg/kg/day) as well as the addition of azathioprine failed to suppress the deterioration. However, an increase in the dose of prednisolone (up to 1 mg/kg/day) enabled us to control hepatitis. This case showed that hepatitis can occur even after discontinuation of ICIs, and that liver biopsy may be useful in the diagnosis. Clinicians should not hesitate to perform liver biopsy for confirmation of the diagnosis.