Sequential Anti-Angiogenic Therapy After Immunotherapy in Advanced Biliary Tract Cancer

Inclusion Criteria: Age 18-75 years at time of enrollment; Histologically or cytologically confirmed advanced or metastatic biliary tract adenocarcinoma (intrahepatic cholangiocarcinoma, extrahepatic cholangiocarcinoma, or gallbladder carcinoma); Unresectable locally advanced or metastatic disease not amenable to curative treatment; At least one measurable lesion according to RECIST version 1.1 criteria; ECOG Performance Status 0-1; Life expectancy ≥ 12 weeks; No prior systemic chemotherapy, immunotherapy, or anti-angiogenic therapy for advanced disease (adjuvant therapy completed \>6 months prior is allowed); Adequate bone marrow function: ANC ≥1.5×10⁹/L, platelets ≥100×10⁹/L, hemoglobin ≥90 g/L; Adequate liver function: Total bilirubin ≤2.5×ULN, ALT and AST ≤3×ULN (or ≤5×ULN if liver metastases present); Adequate renal function: Serum creatinine ≤1.5×ULN or creatinine clearance ≥50 mL/min; Signed informed consent. Exclusion Criteria: Mixed histology tumors or neuroendocrine components; Active central nervous system metastases (treated and stable metastases \>4 weeks allowed); History of other malignancies within 5 years (except adequately treated basal cell carcinoma, squamous cell carcinoma of skin, or carcinoma in situ); Active autoimmune disease requiring systemic treatment; History of severe allergic reactions to monoclonal antibodies or study drug components; Uncontrolled hypertension (\>140/90 mmHg despite medication); Significant cardiovascular disease including unstable angina, myocardial infarction within 6 months, or NYHA Class III-IV heart failure; Active bleeding or bleeding tendency, thrombosis, or use of anticoagulants; Major surgery within 4 weeks or minor surgery within 2 weeks; Active infection requiring systemic treatment; Pregnancy or breastfeeding; HIV infection, active hepatitis B or C infection; Psychiatric illness that would limit compliance with study requirements.