A Study to Evaluate the Pharmacokinetics, Efficacy, and Safety of Subcutaneous Administration of the Fixed-Dose Combination of Pertuzumab and Trastuzumab in Combination With Chemotherapy in Participants With HER2-Positive Early Breast Cancer

Inclusion Criteria:

- Ability to comply with the study protocol, in the investigator's judgment

- Eastern Cooperative Oncology Group (ECOG) Performance Status ≤1

- Female and male patients with Stage II - IIIC (T2-T4 plus any N, or any T plus N1-N3,
M0), locally advanced, inflammatory, or early-stage, unilateral, and histologically
confirmed invasive breast cancer

- Primary tumor >2 cm in diameter, or node-positive disease (clinically or on imaging,
and node positivity confirmed with cytology and/or histopathology)

- HER2-positive breast cancer confirmed by a central laboratory prior to study
enrollment. HER2-positive status will be determined based on pretreatment breast
biopsy material.

- Hormone receptor status of the primary tumor, centrally confirmed

- Patient agreement to undergo mastectomy or breast conserving surgery after neoadjuvant
therapy

- Availability of formalin-fixed, paraffin-embedded (FFPE) tumor tissue block for
central confirmation of HER2 and hormone receptor status and additional biomarker
research

- Baseline left ventricular ejection fraction (LVEF) ≥55% measured by echocardiogram
(ECHO) or multiple-gated acquisition scan (MUGA)

- For women of childbearing potential (WOCBP) who are sexually active: agreement to
remain abstinent or use one highly effective non-hormonal contraceptive method with a
failure rate of <1% per year, or two effective non-hormonal contraceptive methods
during the treatment period and for 7 months after the last dose of HER2-targeted
therapy, and agreement to refrain from donating eggs during this same period

- For men: men must remain abstinent or use a condom with a spermicidal product during
the treatment period and for 7 months after the last dose of HER2-targeted therapy to
avoid exposing the embryo. Men must refrain from donating sperm during this same
period.

- A negative serum pregnancy test must be available prior to randomization for WOCBP,
unless they have undergone surgical sterilization

- No major surgical procedure unrelated to breast cancer within 28 days prior to
randomization or anticipation of the need for major surgery during the course of study
treatment

Exclusion Criteria:

- Stage IV (metastatic) breast cancer

- Patients with a history of invasive breast cancer

- Patients with a history of concurrent or previously treated non-breast malignancies
except for appropriately treated 1) non-melanoma skin cancer and/or 2) in situ
carcinomas, including cervix, colon, and skin

- Patients who have received any previous systemic therapy for treatment or prevention
of breast cancer, or radiation therapy for treatment of cancer

- Patients who have a past history of ductal carcinoma in situ or lobular carcinoma in
situ if they have received any systemic therapy for its treatment or radiation therapy
to the ipsilateral breast

- Patients with high-risk for breast cancer who have received chemo-preventative drugs
in the past are not allowed to enter the study

- Patients with multicentric breast cancer, unless all tumors are HER2-positive

- Patients with bilateral breast cancer

- Patients who have undergone an excisional biopsy of primary tumor and/or axillary
lymph nodes

- Axillary lymph node dissection prior to initiation of neoadjuvant therapy

- Sentinel lymph node biopsy prior to neoadjuvant therapy

- Treatment with any investigational drug within 28 days prior to randomization

- Serious cardiac illness or medical conditions

- Inadequate bone marrow function, renal function or impaired liver function

- Current severe, uncontrolled systemic disease that may interfere with planned
treatment

- Pregnant or breastfeeding, or intending to become pregnant during the study or within
7 months after the last dose of HER2-targeted therapy

- Any serious medical condition or abnormality in clinical laboratory tests that, in the
investigator's judgment, precludes the patient's safe participation in and completion
of the study

- Known active liver disease, for example, active viral hepatitis infection, autoimmune
hepatic disorders, or sclerosing cholangitis

- Concurrent, serious, uncontrolled infections, or known infection with HIV

- Known hypersensitivity to study drugs, excipients, and/or murine proteins

- Current chronic daily treatment with corticosteroids

- History of other malignancy within 5 years prior to screening, except for
appropriately treated carcinoma in situ of the cervix, colon, skin, and/or
non-melanoma skin carcinoma

- History of ventricular dysrhythmias or risk factors for ventricular dysrhythmias, such
as structural heart disease, coronary heart disease, clinically significant
electrolyte abnormalities, or family history of sudden unexplained death or long QT
syndrome