Hepatitis B virus (HBV) is a hepatotropic virus which can lead to acute and chronic hepatitis B. Cirrhosis, hepatocellular carcinoma or liver failure may be consequences of long-term chronic infection. At global level, the notification rate of newly diagnosed hepatitis B infections was 16 per 100,000 population in 2022 [1]. In Brazil, the notification rate of hepatitis B was 5.5 per 100,000 population in 2023 [2].

The natural history of HBV includes episodes of viral reactivation, which predominantly occur in the context of immunosuppressive conditions [3]. HBV reactivation can occur in patients with autoimmune disorders, human immunodeficiency virus (HIV) infection and solid organ transplant, including those exposed to anti-cancer chemotherapy and immunosuppressive or immunomodulatory therapies [4]. Briefly, this reactivation is the sudden reappearance or increased replication of HBV-DNA, which can lead to liver damage ranging from subclinical to severe, as well as to early interruption or delay of cancer treatment, with a serious impact on prognosis. HBV reactivation poses a particularly concerning risk for cancer patients [3], [5].

According to the Global Cancer Observatory, the incidence of cancer in 2022 was 19,976,499 cases [6]. The American Society of Clinical Oncology, the European, the Asian Pacific and the American Associations for the Study of the Liver, among others, recommend testing for HBV markers before cancer treatments. However, HBV infection can be prevented by safe, effective and well-tolerated vaccination, as prophylactic vaccines provoke neutralizing antibodies against HBV and confer long-term immunity [7]. Evidence indicates that the recombinant vaccines can provide a 95 % of sero-protection against HBV infection to healthy infants, children and young adults. In adults older than 60 years, sero-protection is around 60 %-70 % [8]. Furthermore, isolated hepatitis B surface antibodies (anti-HBs) are the only serological marker of hepatitis B detected in those who have acquired immunity through vaccination, with high-titer anti-HBs being the most effective strategy for protecting the body from HBV infection [7], [8].

It is important to vaccinate cancer patients to avoid HBV infection and, consequently, the risk of reactivation and its deleterious effects. This study aimed to investigate the prevalence of anti-HBs, whose meaning is the vaccine-induced immunity to hepatitis B, in patients with solid tumors or hematological malignancies.