Optimal Corticosteroid Therapy Based on Liver Biopsy for Severe Immune-Mediated Hepatitis During Pembrolizumab Treatment: A Case Report.

Immune checkpoint inhibitors (ICIs), including pembrolizumab, are widely used to treat advanced non-small cell lung cancer; however, they are associated with immune-related adverse events, including immune-mediated hepatitis. Although systemic corticosteroids are recommended as first-line therapy for severe immune-mediated hepatitis, the optimal initial dose remains unclear, and current guidelines specify a wide range of doses. Herein, we report the case of a 76-year-old man with lung adenocarcinoma, a history of resolved hepatitis B virus infection, ulcerative colitis in long-term remission, and latent hereditary spherocytosis who developed grade 3 immune-mediated hepatitis during pembrolizumab monotherapy. Liver biopsy revealed moderate lobular necroinflammation consistent with immune-mediated hepatitis. Based on these histopathological findings, prednisolone at 0.3 mg/kg/day was initiated. Liver enzyme levels improved rapidly, and pembrolizumab was subsequently resumed without recurrence of immune-mediated hepatitis. This case highlights the diagnostic and therapeutic value of liver biopsy in patients with severe immune-mediated hepatitis. Histopathological assessment of inflammatory severity and bile duct involvement may contribute to individualized corticosteroid dosing, promote early recovery, and support safe ICI rechallenge.