Gut Microbiota-Mediated Molecular Events in Hepatocellular Carcinoma: From Pathogenesis to Treatment

Background/Objectives: Hepatocellular carcinoma (HCC) is one of the most common causes of cancer and cancer-related death worldwide. Beyond the well-known factors influencing the risk of HCC, experimental data from animal models and observational human studies support a significant role of the gut microbiota (GM) in HCC initiation and progression. Dysbiosis and increased intestinal permeability synergistically disrupt the ‘gut–liver axis,’ exposing the liver to bacterial metabolites and microbial-associated molecular patterns, thereby contributing to hepatocarcinogenesis. While these findings have expanded our understanding of HCC pathogenesis, a critical translational gap persists as most data derive from preclinical settings, with limited validation in large-scale clinical studies. Methods: This narrative review aimed to contextualise the current evidence on the GM-HCC axis and its clinical translatability. A literature search was conducted in PubMed/MEDLINE, Scopus, and Web of Science up to July 2025 using Medical Subject Headings and related keywords, including HCC, GM, dysbiosis, intestinal permeability, gut–liver axis, microbial metabolites, inflammation/immune modulation, and microbiota-targeted interventions (probiotics, antibiotics, and faecal microbiota transplantation). Reference lists of relevant articles were also screened to identify additional studies. Results: Preclinical models consistently indicate that dysbiosis and impaired gut barrier function can promote hepatic inflammation, immune dysregulation, and pro-tumorigenic signalling through microbe-derived products and metabolite perturbations, supporting a contributory role of the GM in hepatocarcinogenesis. In humans, HCC and advanced chronic liver disease are associated with altered microbial composition and function, increased markers of intestinal permeability, and changes in bile acid and other metabolite profiles; however, reported signatures are heterogeneous across cohorts and analytical platforms. Conclusions: The GM is a biologically plausible and experimentally supported contributor to HCC initiation and progression, with potential for biomarker development and therapeutic targeting. However, clinical translation is limited by predominantly preclinical/associative evidence, interindividual variability, and non-standardised microbiome methods. Large longitudinal studies and adequately powered randomised trials are needed to establish causality, validate biomarkers, and determine whether GM modulation improves HCC prevention, detection, stratification, or outcomes.