Reactivation of hepatitis B virus during targeted therapies for cancer and immune-mediated disorders.

INTRODUCTION: Targeted therapies have gained popularity in the treatment of several oncologic and immune-mediated diseases. Immunosuppression caused by these drugs has been associated to reactivation of hepatitis B virus (HBV) in both hepatitis B surface antigen (HBsAg) positive patients (overt infection) and HBsAg negative/anti-hepatitis B core antigen (anti-HBc) positive carriers (resolved infection), leading to premature discontinuation of therapy and potentially fatal hepatitis. AREAS COVERED: This review summarizes the evidence of HBV reactivation in patients with overt or resolved HBV infection undergoing targeted therapies for cancer or immune-mediated disorders, providing recommendations for the management of these patients. EXPERT OPINION: The risk of HBV reactivation relies on the immunosuppressive potency and duration of these therapies, the underlying disease and the virological patient's profile. However, HBV reactivation is preventable by screening for HBV markers in all patients scheduled to receive targeted therapies, assessing the virological profile and patient's clinical state, followed by appropriate antiviral treatment or prophylaxis in those patients at high risk of HBV reactivation. Close monitoring of HBV carriers at low risk of reactivation is warranted with the aim to start antiviral therapy as soon as HBV reactivates.