Hepatitis B (HBV) reactivation and hepatitis flare induced by cytotoxic chemotherapy is common in cancer patients who have chronic HBV infection. Lymphoma patients who had previous infected by HBV but negative for HBsAg have a the risk of HBV reactivation during chemotherapy, but prophylactic antiviral treatment is not a routine by current American Association for the Study of Liver Diseases (AASLD) guideline. Prophylactic entecavir might reduce the risk of HBV reactivation in such patients.