Hepatocellular carcinoma (HCC) is a severe health problem and has become the second leading cause of cancer mortality globally, accounting for 782,000 deaths annually (Bray et al., 2018). The hepatitis B virus (HBV) is the leading cause of cirrhosis and HCC worldwide (El-Serag, 2012). Cirrhosis affects approximately 80% of patients with a subsequent diagnosis of HCC. However, most patients are diagnosed at an advanced stage, with limited treatment options and a low survival rate (Balogh et al., 2016). Current antiviral therapies, such as nucleos(t)ide analogs [NA(s)], are efficacious in inhibiting viral replication, improving liver inflammation, and reducing HCC incidence (Chang et al., 2010; Marcellin et al., 2013). Several studies have reported that antiviral therapy can attenuate, but not completely eliminate the risk of HCC in patients with hepatitis B-related cirrhosis (HBC) (Lee and Ahn, 2016). Despite HBV replication decrease, antiviral therapy alone may be insufficient to prevent HCC. Because of the growing incidence and high mortality rate of HCC, new treatments or prophylactic strategies are urgently needed to lower the risk of HCC.

Probiotics, as live microorganisms, provide health benefits to the host when administered in adequate amounts (Wan and El-Nezami, 2018). Recent studies have reported that probiotics could be used as an alternative for cancer prevention and treatment (Yu and Li, 2016; Singh et al., 2021). Probiotics can regulate the intestinal microflora and maintain the balance in the microbiota ecosystem (Mendoza, 2019). Probiotics influence various biological processes associated with cancer, such as inflammation, oxidative stress, apoptosis, proliferation, and metastasis (Thilakarathna et al., 2021). In addition, probiotics are reported to play an important role in cancer prevention by regulating the microbiome and immune response (Feng et al., 2018). Therefore, clinical trials on the modulation of microbiota dysbiosis by probiotics will contribute to the clinical application of probiotics in the future management of several cancer types.

Multiple researchers have reported that patients with HBC have an altered gut microbiota and significantly greater plasma endotoxin levels than healthy individuals (Qin et al., 2014; Chen et al., 2021). Microbial dysbiosis and endotoxemia are important contributing factors to cirrhosis in HCC (Wan and El-Nezami, 2018). Probiotics have an antiviral activity that slows HCC progression by preventing chronic HBV infection (Lee et al., 2013; Thilakarathna et al., 2021). In an animal study, VSL#3 treatment reduced liver inflammation and restored intestinal homeostasis, preventing cirrhosis progression to HCC (Zhang et al., 2012; Li et al., 2016). Considering the increasing use of probiotics and incidence of HCC, the potential link between probiotics and HCC is an important issue to investigate. However, few studies have reported the effects of adjuvant probiotic therapy on the risk of HCC in patients with HBC in clinical practice. Propensity score matching (PSM) has been used to reduce bias caused by potential confounding factors between groups (Rusthoven et al., 2016; Tian et al., 2022). PSM is an effective statistical method to explore the efficacy of probiotics and HCC occurrence in patients with HBC.

Therefore, we used PSM to investigate the association between probiotic therapy and the risk of HCC among patients with HBC and to provide clinical evidence for probiotics as adjuvant therapy in these populations.

HCC is commonly associated with cirrhosis, and early detection is an excellent way to enhance patients’ longevity. The gut microbiota is an essential intestinal ecosystem; its dysbiosis can disrupt intestinal homeostasis and lead to harmful bacterial overgrowth, causing liver fibrosis, cirrhosis, and HCC. Growing evidence suggests that microbial imbalance causes cancer via various pathways involving inflammation and immunological dysregulation (Plottel and Blaser, 2011; Zhang et al., 2020a). Probiotics are new adjuvant therapies to prevent and reduce the risk of HCC (Wan and El-Nezami, 2018). Endotoxemia and the number of bacterial species can be reduced by administering Bifidobacteria and Lactobacilli (Tandon et al., 2009; Rincón et al., 2014). In this study, we observed a significant inverse association between probiotics use and the risk of HCC in patients with HBC on antiviral therapy. Furthermore, the administration of probiotics reduced the incidence of HCC in a dose-dependent manner.

Several studies have found a close association between gut microbiota alterations and HBC and HCC. Studies have shown that probiotics reduce the length of hospital stay, improve portal hypertension and associated complications, and lower inflammatory factors while causing no adverse events (Dhiman et al., 2014; Rincón et al., 2014). Herein, probiotics were found to be an independent protective factor against HCC in patients with HBC. Probiotic use was associated with a significantly lower risk of HCC, regardless of whether PSM was performed (both P < 0.001). Additionally, the risk reduction of HCC showed a dose-response relationship in the unmatched and matched cohorts. The uncorrected HR for overall probiotic prescription after PSM was 0.70 (95% CI: 0.59–0.83), while the aHR was 0.59 (95% CI: 0.34–0.81). With non-probiotics users as controls, the aHRs were 0.58 (95% CI: 0.33–1.01), 0.28 (95% CI: 0.14–0.56), and 0.12 (95% CI: 0.03–0.52) for 28–89, 90–180, and >180 cDDD, respectively, In a recent study, the high-dose probiotic VSL#3 reduced the risk of lesions in mice as compared to low-dose probiotics or no therapy (Li et al., 2016), indicating that HCC risk decreased as the cumulative dose of probiotics increased. Therefore, probiotic therapy may improve prognosis by reducing HCC morbidity and mortality.

The association between microbiota and the host plays a crucial role in the pathogenesis of HCC. Altering the composition of the intestinal flora can limit bacterial translocation, promote gut microflora balance, and prevent HCC progression (Zhang et al., 2012b). Sandler et al. reported that liver disease severity is related to bacterial translocation and overgrowth (Sandler et al., 2011). In the present study, probiotic users benefited significantly, especially patients with CTP B and C classes. A similar effect of probiotics use was demonstrated in our previous study in patients with cirrhosis (Zhang et al., 2020b). The MELD score is a parameter of a liver function used to assess the prognosis of patients with cirrhosis (Bernardi et al., 2011). Probiotics users had a lower HCC risk than non-probiotics users, regardless of MELD score < 10 or ≥ 10. However, the statistical difference between the two groups was more pronounced when the MELD score was ≥ 10. Preveden et al. previously showed that changes in the gut microflora are affected by liver disease stage (Preveden et al., 2017). Patients with advanced MELD and CTP scores show greater perturbations in microbial toxins, lipopolysaccharide secretion, and proinflammatory cytokine levels (Rayes et al., 2002; Rayes et al., 2005). Therefore, these patients were positively correlated with the benefit.

Probiotic therapy is a novel regimen for chronic liver diseases complicated by gut dysbiosis. Hepatocarcinogenesis is aided by gut microbial dysbiosis. Accumulating evidence has suggested that the gut–liver axis plays a key role in the progression of cirrhosis and HCC (Wiest et al., 2017; Ohtani and Kawada, 2019). Progress has been made in understanding the relationship between microbiota dysbiosis and carcinogenesis. Several experimental studies have reported that probiotics positively impact hosts (Patel and DuPont, 2015; Elzouki, 2016). The mechanism by which probiotics increase HCC risk may be associated with the following: (1) Gut microbiota modulation. The production of short-chain fatty acids (SCFAs) such as butyrate may reverse intestinal dysbiosis and reduce the risk of HCC (Li et al., 2016). Some studies reported that probiotics prevent carcinogenesis, by producing SCFAs, controlling gut microbiota composition, and improving gut barrier integrity (LeBlanc et al., 2017). (2) Improvement of gut barrier integrity. Gut bacterial dysbiosis damages the intestinal barrier, promotes bacterial translocation, and, subsequently, induces inflammatory responses (Zhang et al., 2012; Bajaj et al., 2018). Probiotics can enhance the intestinal barrier and decrease inflammation, thereby inhibiting HCC progression (Zhang et al., 2012). (3) Immune regulation and anti-inflammatory role. Gut microbial dysbiosis triggers a pro-inflammatory immune response and cancer progression (Singh et al., 2021). A study has reported that probiotics promote the growth of beneficial microbes, producing anti-inflammatory metabolites with antitumor activity (Li et al., 2016). (4) Antimicrobial effect. Bacterial translocation leads to endotoxemia, which results in portal hypertension and liver cell damage, thus contributing to HCC occurrence (Tao et al., 2015). Probiotics can release antimicrobial molecules, reduce bacterial translocation and overgrowth, and improve endotoxemia (Seki and Schnabl, 2012; Petschow et al., 2013). Thus, these possible mechanisms explain how probiotics reduce the risk of HCC in patients with HBC.

To the best of our knowledge, this is the first observational study to investigate the benefits of probiotics in reducing HCC risk in a population-based cohort of patients with HBC on antiviral therapy. However, this study had several limitations. First, this was an observational retrospective study; thus, potential confounding risk factors may have existed. Despite careful PSM, we cannot exclude the possibility of residual confounding resulting from unmeasured variables, such as diet, coffee, duration of antiviral therapy, and course of cirrhosis. Further prospective randomized controlled trials are required to determine the impact of these risk factors on developing HCC. Second, owing to the single-center study design, the number of patients was limited. Large-sample, multicenter studies need to be conducted in the future. Third, due to the cross-use of probiotics during the study period, we could not further compare the efficacy of different probiotics. We will examine the efficacy of different probiotics in preventing HCC in the future. In addition, the side effects of probiotics for patients were difficult to evaluate in this study. Before probiotic therapy is used to prevent HCC in practice, prospective trials should be conducted to assess its efficacy and safety. Lastly, gut microbiota data were not available in our database; therefore, we did not analyze the association between the microbiota population and HCC risk. We are currently conducting a prospective study using metabonomics, transcriptomics, and proteomic analyses to determine the relationship between the microbiome and carcinogenesis.

This study demonstrated that probiotics might reduce the risk of HCC occurrence in patients with HBC in a dose-dependent manner. However, further prospective studies are required to confirm the preventive effects of probiotics against HCC.

The original contributions presented in the study are included in the article/ Supplementary Material . Further inquiries can be directed to the corresponding author.

The studies involving human participants were reviewed and approved by The Ethical Review Committee of the Beijing Ditan Hospital. Written informed consent for participation was not required for this study in accordance with the national legislation and the institutional requirements.

XW and KS conceived and designed the project. KS, QZ, YZ, and YB collected the data. KS and QZ analyzed and interpreted the data. KS drafted the manuscript. YZ, YB, and XZ was responsible for manuscript modification. All authors contributed to the article and approved the submitted version.