Anti-HER2 Bispecific Antibody Zanidatamab (ZW25) Activity in Combination With Chemotherapy With/Without Tislelizumab

Key Inclusion Criteria:

1. Disease diagnosis and prior treatment:

2. Cohort 1 (the first-line breast cancer treatment cohort):

• Female participants with histologically or cytologically confirmedunresectable, locally advanced, recurrent or metastatic adenocarcinoma ofthe breast and candidate for chemotherapy. Locally recurrent disease mustnot be amenable to resection with curative intent.
• Human epidermal growth factor receptor 2 (HER2) IHC 3+ or in situhybridization positive on the archival tumor tissue or fresh biopsysample.
• Have not received previous systemic anticancer therapy for locallyadvanced unresectable or metastatic disease.

2. Cohort 2 (the first-line gastric/gastroesophageal junction adenocarcinomatreatment cohort):

• Histologically or cytologically confirmed unresectable, locally advanced,recurrent or metastatic adenocarcinoma of the stomach or gastroesophagealjunction
• HER2 IHC 3+ or HER2 IHC 2+ together with in situ hybridization positive onthe archival tumor tissue or fresh biopsy sample.
• Have not received previous systemic anticancer therapy for locallyadvanced unresectable or metastatic disease, including any approved orinvestigational estimated glomerular filtration rate (EGFR) or anti-HER2agents or vaccines, cytotoxic chemotherapy or checkpoint inhibitors

2. At least 1 measurable lesion as defined per RECIST Version 1.1

3. Eastern Cooperative Oncology Group (ECOG) Performance Status ≤ 1

4. Adequate organ function

5. Left ventricular ejection fraction (LVEF) ≥ 50% at baseline as determined by eitherechocardiogram or multigated acquisition scan (MUGA) (echocardiogram is thepreferred method) within 28 days before the first dose of study drug

Key Exclusion Criteria:

1. Prior therapy with an anti-PD-1, anti-PD-L1, anti-PD-L2 or any other antibody ordrug specifically targeting T-cell co-stimulation or checkpoint pathways

2. History of approved or investigative tyrosine kinase/HER inhibitors in any treatmentsetting a. except trastuzumab with or without pertuzumab used in neoadjuvant or adjuvantsetting for Cohort 1

3. Active leptomeningeal disease, untreated or uncontrolled brain metastasis

4. Any active malignancy ≤ 2 years before the first dose of study drug, except for thespecific cancer under investigation in this trial and any localized cancer that hasbeen treated curatively (eg, resected basal or squamous cell skin cancer,superficial bladder cancer, carcinoma in situ of the cervix)

5. Any condition that required systemic treatment with either corticosteroids (> 10 mgdaily of prednisone or equivalent) or other immunosuppressive medication ≤ 14 daysbefore the first dose of study drug

Note: Participants who are currently or have previously been on any of the following steroid regimens are not excluded:

1. Adrenal replacement steroid (dose ≤ 10 mg daily of prednisone or equivalent)

2. Topical, ocular, intra-articular, intranasal, or inhaled corticosteroid with minimalsystemic absorption

3. Short course (≤ 7 days) of corticosteroid prescribed prophylactically (eg, forcontrast dye allergy) or for the treatment of a non-autoimmune condition (eg,delayed-type hypersensitivity reaction caused by contact allergen)

NOTE: Other protocol defined Inclusion/Exclusion criteria may apply.