Abstract
An 82-year-old man was treated with ipilimumab and nivolumab for malignant pleural mesothelioma. Although he was previously treated with prednisolone (1 mg/kg/day) for immune-related adverse event (irAE) hepatitis by a previous doctor, he still had worsening liver function and was transferred to our hospital. Blood tests and imaging findings were negative for autoimmune and infectious hepatitis, and liver biopsy results were consistent with irAE hepatitis. Steroid pulse therapy improved liver function, but tapering to prednisolone (1 mg/kg/day) again worsened his liver function. Concomitant use of mycophenolate mofetil was initiated, but no improvement in liver function was observed, therefore azathioprine, a thiopurine immunosuppressant, was administered in combination with steroids. During the course of treatment, hepatic dysfunction due to azathioprine was suspected, and the concomitant use of mercaptopurine and prednisolone was started. Afterward, the liver function improved, and the prednisolone dose was gradually reduced to 10 mg/day. This is a rare case in which a thiopurine-based immunosuppressant was effective against irAE hepatitis, therefore thiopurine-based immunosuppressants may be effective against steroid-refractory hepatitis.