Distinct gut microbiota but common metabolomic signatures between viral and MASLD HCC contribute to outcomes of combination immunotherapy

BACKGROUND AND AIMS: Gut microbiota could modulate the outcome of cancer immunotherapy, including HCC. Although metabolic dysfunction-associated steatotic liver disease-related HCC (MASLD-HCC) and viral hepatitis-related HCC (V-HCC) exhibit different tumor microenvironments and gut microbiome composition, both respond to combination immunotherapy. This study aimed to investigate whether distinct microbiota/metabolomic signatures are associated with outcomes of combination immunotherapy in MASLD-HCC and V-HCC, separately. APPROACH AND RESULTS: Between January 2021 and April 2024, 77 V-HCC patients and 25 with MASLD-HCC initiating first-line combination immunotherapy were prospectively enrolled. Pre-treatment fecal microbiota/metabolites and serum cytokines/chemokines were analyzed in association with durable tumor response, overall survival (OS) and progression-free survival (PFS). MASLD-HCC patients showed predominant fecal Bacteroides ovatus , Kluyvera georgiana , Klebsiella oxytoca , and Enterococcus faecium , with lower levels of short-chain fatty acids (SCFAs) and ursodeoxycholic acid (UDCA) compared to V-HCC. Durable responders (DRs) of MASLD-HCC had enriched Mediterraneibacter gnavus ATCC 29149 and significantly higher SCFAs (acetate, propionate, butyrate, and isobutyrate) and UDCA. In contrast, V-HCC-DRs were characterized by predominant Bifidobacterium and similarly enriched SCFAs. In both MASLD-HCC and V-HCC, fecal acetate level was a common significant predictor of DR, PFS, and OS. Patients with higher acetate levels had significantly longer OS (median: 25.2 vs. 11.3 mo; p <0.001) and PFS (median: 15.3 vs. 4.2 mo; p <0.001). CONCLUSIONS: Distinct gut microbiota, but shared beneficial metabolites, particularly fecal acetate, are associated with durable response to combination immunotherapy and improved survival in both MASLD-HCC and V-HCC. Fecal acetate may serve as a potential biomarker and therapeutic target for optimizing HCC treatment.