Pembrolizumab With or Without Lenvatinib or Chemotherapy in First-Line Treatment of Advanced Biliary Tract Cancer

Drug: Pembrolizumab Pembrolizumab 200 mg will be administered intravenously once every three weeks, with intravenous infusion on Day 1 of each cycle. Drug: Lenvatinib Oral Product The dose of lenvatinib is 12mg/day for patients with a body weight of ≥60 kg, and 8mg/day for patients with a body weight of \<60 kg, taken once daily. Drug: Chemotherapy GEMOX regimen: Gemcitabine 1000mg/m2 will be administered intravenously over 30 minutes on Day 1 and Day 8; Oxaliplatin 100mg/m2 will be administered intravenously over 2 hours on Day 1, and the cycle will be repeated every 3 weeks.

Pembrolizumab and Lenvatinib

Pembrolizumab and Gemox Chemotherapy（Gemcitabine and Oxaliplatin）