Zanidatamab (ZW25), a bispecific antibody, simultaneously binds to 2 HER2 epitopes: ECD4, the trastuzumab binding domain, and ECD2, the pertuzumab binding domain was recently approved for the treatment of previously treated, unresectable, or metastatic HER2-positive (IHC3+) biliary tract cancer (BTC), based on findings from the HERIZON-BTC-01 trial (NCT04466891). The gene discussed is ERBB2; the disease is biliary tract cancer.