Rilvegostomig + Chemotherapy as Adjuvant Therapy for Biliary Tract Cancer After Resection (ARTEMIDE-Biliary01)

Inclusion Criteria: * Histologically confirmed adenocarcinoma of the biliary tract (intrahepatic or extrahepatic cholangiocarcinoma (CCA) or muscle invasive gallbladder cancer (GBC)) after macroscopically complete resection (R0 or R1) * Provision of a tumor sample collected at surgical resection. * Randomization within 12 weeks after resection with adequate healing and removal of drains. * Confirmed to be disease-free by imaging within 28 days prior to randomization. * Eastern Cooperative Oncology Group performance status of 0 or 1 Exclusion Criteria: * Participants with locally-advanced, unresectable, or metastatic disease at initial diagnosis. * Ampullary cancer, neuroendocrine, mixed neuroendocrine and non-neuroendocrine neoplasms and nonepithelial tumors. * Any anti-cancer therapy for BTC prior to surgery * Active or prior documented autoimmune or inflammatory disorders or any severe or uncontrolled systemic disease * Current or prior use of immunosuppressive medication within 14 days before the first dose * Thromboembolic event within 3 months * Active HBV or HCV infection unless treated.