Envafolimab With Chemotherapy and Simvastatin in Advanced Biliary Tract Cancer

Inclusion Criteria: * Age : ≥18 years old. * Diagnosis : Histologically confirmed unresectable, locally advanced, or metastatic biliary tract adenocarcinoma (including intrahepatic cholangiocarcinoma, extrahepatic cholangiocarcinoma, and gallbladder cancer). * Prior Treatment :Treatment-naïve for unresectable/metastatic disease at initial diagnosis, OR Disease recurrence ≥6 months after curative surgery or adjuvant therapy. * Performance Status : ECOG PS 0 or 1. * Measurable Disease : At least one radiologically measurable lesion per RECIST 1.1 (tumor lesion ≥10 mm on CT scan, lymph node ≥15 mm in short axis). * Organ Function : No severe functional impairment of heart, lung, brain, or other vital organs. Exclusion Criteria: * Disease Type : Ampulla of Vater cancer. * Autoimmune Disease : Active or previously documented autoimmune/inflammatory disorders. * Allergy : Hypersensitivity to any study drug (Envafolimab, gemcitabine, cisplatin, or simvastatin). * Liver Function : Decompensated liver dysfunction. * Psychiatric History : Severe psychiatric disorders. * Recent Trials : Participation in other drug/device trials within 4 weeks prior to enrollment. * Compliance : Inability to adhere to protocol requirements or follow-up schedule. * Investigator's Discretion : Any other condition deemed unsuitable for participation by the investigator.