The purpose of this study is to evaluate the efficacy and safety of Zanidatamab plus CisGem (Cisplatin and Gemcitabine) with or without the addition of a programmed death protein 1/ligand-1 (PD-1/L1) inhibitor (physician's choice of either Durvalumab or Pembrolizumab, where approved under local regulations) as first line of treatment for participants with human epidermal growth factor receptor 2 (HER2)-positive biliary tract cancer.
Histologically- or cytologically-confirmed Biliary Tract Cancer (BTC), including Gallbladder Cancer (GBC), Intrahepatic Cholangiocarcinoma (ICC), or Extrahepatic Cholangiocarcinoma (ECC).
Locally advanced unresectable or metastatic BTC and not eligible for curative resection, transplantation, or ablative therapies.
Received no more than 2 cycles of systemic therapy which is limited to Cisplatin and Gemcitabine (CisGem) with or without a PD-1/L1 inhibitor (physician's choice of durvalumab or pembrolizumab, where approved under local regulations) for advanced unresectable or metastatic disease.
HER2-positive disease (defined as IHC 3+; or IHC 2+/ ISH+) by IHC and in situ Hybridization (ISH) assay (in participants with IHC 2+ tumors) at a central laboratory on new biopsy tissue or archival tissue from the most recent biopsy.
Prior treatment with a HER2-targeted agent
Prior treatment with checkpoint inhibitors, other than durvalumab or pembrolizumab
The following BTC histologic subtypes are excluded: small cell cancer, neuroendocrine tumors, lymphoma, sarcoma, mixed tumor histology, and mucinous cystic neoplasms detected in the biliary tract region.
Use of systemic corticosteroids.