RecruitingDrug trialHepatic Arterial Infusion Chemotherapy Plus Envafolimab and Lenvatinib for First-Line Unresectable Advanced Biliary Tract CancerAdvanced biliary tract cancer has a poor prognosis and limited efficacy with current regimens. This multicenter single-arm phase Ib/II trial explores the efficacy and safety of HAI-GP chemotherapy combined with intraoperative arterial envafolimab and lenvatinib as first-line therapy for unresectable BTC. It conducts dose exploration to confirm the optimal dosage and evaluates clinical outcomes, aiming to establish a better comprehensive treatment strategy.