Hepatitis B Virus Reactivation After 23 Months of Rituximab-based Chemotherapy in an HBsAg-negative, Anti-HBs-positive Patient With Follicular Lymphoma

A 72-year-old female negative for hepatitis B surface antigen (HBsAg) and positive for antibody to hepatitis B surface antigen (anti-HBs) was diagnosed to have follicular lymphoma in 2006. Seventeen cycles of rituximab-based chemotherapy were administered over 23 months. Twelve days after the last cycle of chemotherapy, serum aminotransferase levels were elevated, and hepatitis serology tests revealed reappearance of HBsAg and hepatitis B e antigen (HBeAg), loss of anti-HBs, and positivity for hepatitis B virus (HBV) DNA. Antiviral treatment with entecavir was administered immediately, and the hepatitis flare was controlled. Rituximab-based chemotherapy can induce HBV reactivation even in HBsAg-negative, anti-HBs-positive patients. Early recognition and prompt antiviral treatment is crucial for patients with HBV reactivation during anticancer therapy.