Key Inclusion Criteria:

1. Sign and date the tissue prescreening informed consent form (ICF), prior to HER2 central testing. Sign and date the main ICF, prior to the start of any trial- specific qualification procedures. Consent to optional PGx prior to any PGx procedures. For participants in the safety run-in phase, a safety run-in ICF needs to be signed and dated prior to the start of any trial-specific qualification procedures.
2. Adults ≥18 years of age on the day of signing the ICF. Follow local regulatory requirements if the legal age of consent for trial participation is >18 years old.
3. Has histologically confirmed diagnosis of epithelial high-grade ovarian, fallopian tube or primary peritoneal carcinoma (including but not limiting to serous, endometrioid, clear cell, carcinosarcoma, mucinous).
4. Is newly diagnosed FIGO Stage III or IV.
5. Has HER2 expression per 2016 ASCO-CAP gastric cancer IHC scoring (3+/2+/1+) guidelines1 by prospective central testing. For participants in the safety run-in phase, HER2 expression assessed by either local (require using ASCO-CAP gastric cancer IHC scoring [IHC 3+/2+/1+] guidelines) or central assessment (if available) is acceptable. Submission of the pathology report is required for participants enrolled based on local HER2 IHC results.
6. Has adequate tumor tissue sample available for assessment of HER2 by central laboratory. Tumor tissue block or sufficient tissue slides are required for HER2 testing and retrospective HRD status determination. Participants in the safety run-in phase who are enrolled based on local HER2 IHC results are recommended to provide tumor tissue sample from the same specimen for central assessment.
7. Has a local HRD or breast cancer gene (BRCA) test result available. Participants with BRCA wildtype will have a local HRD test results, as applicable.
8. Has received standard of care bevacizumab in combination with front line platinum based chemotherapy as per approved indication and clinical guidelines and is eligible to continue single agent bevacizumab maintenance per standard of care and investigator discretion.

Key Exclusion Criteria:

1. Has ovarian, fallopian tube, or peritoneal cancer of non-epithelial origin.
2. Has a BRCA mutation as per local test.
3. Participant to receive PARP inhibitor as maintenance per standard of care and investigator discretion. Reasons for which the participant is not eligible for PARP inhibitor will be recorded in the eCRF as follows: HRD negative HRD positive with SD as best response after platinum HRD positive non-serous histology HRD tested, but inconclusive HRD positive but safety concern (safety concern to be specified).
4. Has a history of severe hypersensitivity reactions to either the drug substances or inactive ingredients in the drug products and other monoclonal antibodies.
5. Previous Cerebral-Vascular Accident, Transient Ischemic Attack or Sub- Arachnoids Hemorrhage within 6 months prior to randomization.
6. Has evidence of bleeding diathesis or significant coagulopathy (in the absence of anticoagulation therapy).
7. Has a history of hemorrhagic disorders, abdominal fistula, gastrointestinal perforation, or active gastrointestinal bleeding within 6 months before randomization.
8. Evidence of active or ongoing bowel obstruction.
9. Has lung-specific intercurrent clinically significant illnesses including, but not limited to, any underlying pulmonary disorder (eg, pulmonary emboli within 3 months of the trial randomization, severe asthma, severe chronic obstructive pulmonary disease, restrictive lung disease, pleural effusion, pneumonectomy, etc.)
10. Has a history of (non-infectious) ILD/pneumonitis that required steroids, has current ILD/pneumonitis, or where suspected ILD/pneumonitis cannot be ruled out by imaging at Screening.
11. Clinically severe pulmonary compromise resulting from intercurrent pulmonary illnesses including, but not limited to, any underlying pulmonary disorder (ie pulmonary emboli within three months of the trial enrollment, severe asthma, severe COPD, restrictive lung disease, pleural effusion etc.), and any autoimmune, connective tissue or inflammatory disorders with potential pulmonary involvement (ie Rheumatoid arthritis, Sjogren's, sarcoidosis etc.), or prior pneumonectomy.