Fulminant hepatitis in a hepatitis B surface antigen‐positive patient with adult T‐cell leukemia‐lymphoma after mogamulizumab monotherapy

Abstract We report a case of fulminant hepatitis in a hepatitis B surface antigen (HBsAg)‐positive patient with aggressive adult T‐cell leukemia‐lymphoma who received monotherapy with an anti‐CCR4 monoclonal antibody, mogamulizumab, with decreased hepatitis B virus (HBV)‐ DNA levels by entecavir prophylaxis. Although HBV reactivation‐related hepatitis was considered in the differential diagnosis, the patient did not meet the conventional criteria for HBV reactivation and was finally diagnosed with drug‐induced hepatitis. Considering that the immunoenhancing effects of mogamulizumab can lead to HBV reactivation‐related hepatitis in HBsAg‐positive patients, we should differentiate drug‐induced hepatitis from HBV reactivation, especially in patients receiving immunomodulatory drugs, if HBV‐DNA levels are reduced by antiviral prophylaxis.