Phase 3 Study of T-DXd and Rilvegostomig Versus SoC in Advanced HER2-expressing Biliary Tract Cancer

Key Inclusion Criteria: * Male and female patients must be at least 18 years of age at the time of signing the informed consent. Other age restrictions may apply as per local regulations. * Unresectable, previously untreated, locally advanced or metastatic biliary tract adenocarcinoma. Prior treatment in the perioperative and/or adjuvant setting is permissible provided there is \> 3 months (90 days) between the end of adjuvant treatment and the diagnosis of locally advanced or metastatic disease. * Histologically confirmed HER2-expressing (IHC 3+ or IHC 2+) BTC. * Patients must provide an FFPE tumor sample that is no older than 3 years for tissue-based IHC staining to centrally determine HER2 expression, PD-L1 status, and other correlatives. * Has at least one target lesion assessed by the Investigator based on RECIST v1.1. (Randomized portion only) * WHO/ECOG performance status of 0 or 1 with no deterioration over the previous 2 weeks prior to baseline or day of first dosing. * Adequate organ and bone marrow function within 14 days before randomization. * Evidence of post-menopausal status or negative serum pregnancy test for females of childbearing potential. * Minimum life expectancy of 12 weeks. Key Exclusion Criteria: * Prior exposure to other HER2 targeting therapies, ADCs, immune checkpoint inhibitors and therapeutic anticancer vaccines. * Histologically confirmed ampullary carcinoma. * Any other medical conditions such as clinically significant cardiac or psycholog…