RecruitingPhase 3Drug trialA Study Comparing the Efficacy and Safety of Zanidatamab to Trastuzumab, Each in Combination With Physician's Choice Chemotherapy, for the Treatment of Participants With Metastatic HER2-positive Breast CancerThe efficacy and safety of zanidatamab in combination with physician's choice of chemotherapy compared with trastuzumab in combination with physician's choice of chemotherapy will be evaluated for the treatment of participants with metastatic HER2-positive breast cancer who have progressed on, or are intolerant to, previous T-DXd treatment.