This study investigates the gut microbiota and metabolites associated with clinical response in patients with biliary tract cancer (BTC) treated with anti-PD-1/PD-L1 immunotherapy. Using metagenomics and metabolomics, researchers analyzed 88 BTC patients who received PD-1/PD-L1 inhibitors between 2018 and 2022. They identified significant differences in bacterial composition and metabolites between patients with durable clinical benefit (DCB) and non-durable clinical benefit (NDB). Key findings include the positive correlation of Alistipes with survival and the negative correlation of Bacilli, Lactobacillales, and Pyrrolidine with survival. Predictive models based on six bacteria, four metabolites, and combinations of three bacteria and two metabolites showed high accuracy in distinguishing DCB and NDB groups. Beta diversity between the groups was significantly different, indicating changes in microbiome composition based on immunotherapy use. The study suggests that gut microbiota and metabolites could serve as potential prognostic and predictive biomarkers for clinical outcomes in BTC patients. The findings highlight the importance of microbiome-metabolite interactions in immunotherapy response and emphasize the need for further research to validate these biomarkers and understand their mechanisms. The study also notes that clinical factors such as hepatitis and vascular invasion influence gut microbiome distribution, and that the Bacteroidetes/Firmicutes ratio is associated with immunotherapy response. Overall, the research underscores the role of the gut microbiome in immunotherapy outcomes for BTC and the potential for microbiome-based strategies to improve treatment efficacy.This study investigates the gut microbiota and metabolites associated with clinical response in patients with biliary tract cancer (BTC) treated with anti-PD-1/PD-L1 immunotherapy. Using metagenomics and metabolomics, researchers analyzed 88 BTC patients who received PD-1/PD-L1 inhibitors between 2018 and 2022. They identified significant differences in bacterial composition and metabolites between patients with durable clinical benefit (DCB) and non-durable clinical benefit (NDB). Key findings include the positive correlation of Alistipes with survival and the negative correlation of Bacilli, Lactobacillales, and Pyrrolidine with survival. Predictive models based on six bacteria, four metabolites, and combinations of three bacteria and two metabolites showed high accuracy in distinguishing DCB and NDB groups. Beta diversity between the groups was significantly different, indicating changes in microbiome composition based on immunotherapy use. The study suggests that gut microbiota and metabolites could serve as potential prognostic and predictive biomarkers for clinical outcomes in BTC patients. The findings highlight the importance of microbiome-metabolite interactions in immunotherapy response and emphasize the need for further research to validate these biomarkers and understand their mechanisms. The study also notes that clinical factors such as hepatitis and vascular invasion influence gut microbiome distribution, and that the Bacteroidetes/Firmicutes ratio is associated with immunotherapy response. Overall, the research underscores the role of the gut microbiome in immunotherapy outcomes for BTC and the potential for microbiome-based strategies to improve treatment efficacy.