The purpose of this study is to see if zanidatamab is safe and effective, when combined with chemotherapy, in treating people who has Human Epidermal Growth Factor Receptor 2 (HER2)-positive, early-stage breast cancer

Inclusion Criteria:

1. Has newly diagnosed Stage II or III histologically confirmed invasive breast carcinoma.

2. Has histologically confirmed HER2-positive breast cancer

3. Has a known hormone receptor (HR) status of the primary tumor

4. Participants with multifocal or multicentric disease are eligible if the largest tumor (which must be larger than or equal to 2 cm in diameter) is HER2-positive, and the treating physician has determined the participant should be treated as HER2-positive.

5. Agrees to undergo a mastectomy or breast conserving surgery (BCS) after neoadjuvant therapy.

6. Has an Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1.

7. Adequate organ function

8. Has an LVEF ≥ 50% as determined by either ECHO or MUGA obtained within 6 weeks prior to randomization.

9. Adequate contraceptive precautions

10. Participants with known HIV are eligible unless:

    1. CD4+ T Cell count is less than or equal to 350 microliters (uL)
    2. Detectable viral load, or
    3. Receiving protease inhibitors or cobicistat

Exclusion Criteria:

1. Has Stage IV (metastatic) breast cancer.
2. Has bilateral breast cancer.
3. Has a history of any severe and/or uncontrolled medical conditions or other conditions that, in the opinion of the investigator, could affect the participant's involvement in the study.
4. Has uncontrolled hypertension
5. Has significant symptoms from peripheral neuropathy
6. Has an active uncontrolled infection
7. Has a history of life-threatening hypersensitivity to monoclonal antibodies or to recombinant proteins or excipients in the drug formulation of zanidatamab or other study interventions.
8. Known active hepatitis B or C infection.
9. Has another malignancy diagnosed within the last 5 years. Exceptions include previously treated non melanomatous skin cancers, carcinoma in-situ, and melanoma in-situ. Participants with prior ipsilateral ductal carcinoma in situ (DCIS) or invasive breast cancer are not eligible.
10. Was treated with surgery, chemotherapy, anti-HER2 therapy, radiation therapy, endocrine therapy, or experimental therapy for invasive breast cancer
11. Is planning to receive concurrent therapy with any other investigational agent or anti-cancer therapy not specified in the protocol
12. Receipt of a live vaccine within 4 weeks prior to enrollment
13. Has a known hypersensitivity to any components of the study interventions, including chemotherapy

In accordance with ICMJE requirements, Jazz Pharmaceuticals may provide qualified external researchers access to individual participant data (IPD) and clinical trial data that underlie the results of this trial upon request. Qualified researchers can submit a request on https://www.jazzpharma.com/science/clinical-trial-data-sharing/ as outlined. Jazz Pharmaceuticals reserves the right not to consider a request. For inquiries about Jazz's data sharing policy contact clinicaldatasharing@jazzpharma.com.