Patients undergoing chemotherapy or immunosuppression should be screened for HBsAg and anti-HBc prior to treatment. Tenofovir can be used as one of the pre-treatment antiviral drugs for chemotherapy or immunosuppression in HBsAg/HBV DNA-positive patients. Tenofovir should be administered at least 2 to 4 weeks before immunosuppressive therapy or chemotherapy, and the patient's condition should be discontinued as appropriate. In patients with single anti-HBc positive patients, the levels of HBsAg, HBV DNA and ALT should be closely monitored when using immunosuppressive agents or cytotoxic drugs. If necessary, drugs such as Tenofovir should be used to prevent HBV infection reactivation.