Risk of Hepatitis B Reactivation Among HBsAg-Negative, Anti-HBc–Positive Breast Cancer Patients Undergoing Chemotherapy

Background Hepatitis B virus (HBV) reactivation is a potential complication in HBsAg-negative, anti-HBc–positive patients receiving immunosuppressive cancer therapy. However, real-world evidence describing reactivation risk in breast cancer populations—particularly in the context of modern systemic regimens—is limited. Methods We conducted Two-center retrospective cohort study of HBsAg-negative, anti-HBc–positive breast cancer patients treated with systemic chemotherapy or targeted agents between 2018 and 2024 in Türkiye. Patients receiving antiviral prophylaxis were excluded. Demographic, oncologic, and virological data—including baseline anti-HBs titers and available serial HBV DNA measurements—were collected. HBV reactivation was defined using international criteria. Results Among 139 eligible patients (mean age 60.1 years), 89.2% were anti-HBs–positive at baseline. Anthracycline-based regimens were administered to 65.5% of the cohort. HBV reactivation occurred in one patient (0.7%; 95% CI, 0.02–3.94%), who lacked protective anti-HBs antibodies and received anthracycline-containing therapy. No reactivations were observed among patients treated with taxanes, HER2-directed agents, CDK4/6 inhibitors, or platinum regimens. Because HBV DNA monitoring was not uniformly performed, subclinical or asymptomatic reactivation events may have been underdetected. Conclusion HBV reactivation was uncommon in this real-world breast cancer cohort, and the single event occurred in a patient with established risk factors. These findings support guideline-aligned, risk-adapted monitoring rather than universal antiviral prophylaxis. However, the low number of events and nonstandardized virological follow-up warrant cautious interpretation and highlight the need for prospective studies using uniform HBV DNA surveillance.