Inclusion Criteria

Key Inclusion criteria:

- Age 18 years or older

- Histologically or cytologically proven adenocarcinoma of the breast

- Subjects who have locally recurrent or metastatic disease with at least one
measurable lesion

- HER2 positive as determined by score of 3+ on immunohistochemistry (IHC) staining or
gene amplification by fluorescence in situ hybridization (FISH).

- Eastern Cooperative Oncology Group (ECOG) performance status (PS) score of 0, 1 or 2

- At least 12 months since prior neoadjuvant or adjuvant chemotherapy

- At least 2 weeks since prior radiotherapy, endocrine therapy, trastuzumab, or
lapatinib, with complete recovery from the effects of these interventions

- Adequate renal function

- Adequate bone marrow function

- Adequate liver function

- Adequate cardiac function

Key Exclusion criteria:

- Prior chemotherapy, biologic therapy, or investigational therapy for locally
recurrent or metastatic HER2+ breast cancer.

- Subjects who have had a prior malignancy other than carcinoma in situ of the cervix,
or nonmelanoma skin cancer

- Prior exposure to > 360 mg/m2 doxorubicin or liposomal doxorubicin, > 120 mg/m2
mitoxantrone, > 90 mg/m2 idarubicin, or > 720 mg/m2 epirubicin

- Inflammatory breast cancer

- Prior history of hypertensive crisis or hypertensive encephalopathy

- Clinically significant cardiovascular impairment

- Subjects with known central nervous system (CNS) disease are not eligible, except for
those subjects with treated brain metastasis.

- Subjects with metastatic disease limited to bone are ineligible unless there is at
least one lytic lesion with identifiable soft tissue components that can be evaluated
by computed tomography (CT) or magnetic resonance imaging (MRI)

- Pulmonary lymphangitic involvement that results in pulmonary dysfunction requiring
the use of oxygen

- History of bleeding diasthesis

- Currently pregnant or breast-feeding.

- Subjects with preexisting Grade 3 or 4 neuropathy. Any peripheral neuropathy must
recover to Grade