To evaluate the efficacy and immune microenvironment changes in treatment-naïve advanced biliary tract cancer (BTC) patients receiving first-line standard therapy with gemcitabine/cisplatin (GemCis) combined with PD-1/PD-L1 inhibitors.
Age ≥18 years.
Histologically confirmed unresectable/metastatic cholangiocarcinoma (intrahepatic, extrahepatic, or gallbladder).
No prior systemic anticancer therapy (chemotherapy, targeted therapy, or immunotherapy).
Planned to receive GemCis+PD-1/PD-L1 inhibitor as standard first-line treatment.
Prior systemic therapy.
Active autoimmune disease requiring immunosuppression.
Active infection requiring IV antibiotics.
HIV-positive or active HBV/HCV infection (HBsAg+ with HBV DNA ≥2000 IU/mL; HCV RNA+).