Inclusion Criteria:

- Adult patients, >/= 18 years of age

- Histologically or cytologically confirmed adenocarcinoma of the breast with
metastatic or locally advanced disease not amenable to curative resection

- HER2-positive as assessed by local laboratory on primary or metastatic tumor

- At least one measurable lesion and/or non-measurable disease evaluable according to
RECIST version 1.1 criteria

- Eastern Cooperative Oncology Group (ECOG) performance status 0 or 1

- Left ventricular ejection fraction (LVEF) of at least 55%

- Life expectancy of at least 12 weeks

Exclusion Criteria:

- Previous systemic non-hormonal anticancer therapy in the metastatic or locally
advanced setting

- Previous approved or investigative anti-HER2 agents in any breast cancer treatment
setting, except trastuzumab and/or lapatinib in the adjuvant or neoadjuvant setting

- Disease progression while receiving trastuzumab and/or lapatinib in the adjuvant or
neoadjuvant setting

- Disease-free interval from completion of adjuvant or neoadjuvant systemic
non-hormonal treatment to recurrent disease of less than 6 months

- History of persistent Grade 2 or higher (NCI-CTC Version 4.0) hematological toxicity
resulting from previous adjuvant or neoadjuvant therapy

- Radiographic evidence of central nervous system (CNS) metastases

- Current peripheral neuropathy of Grade 3 or greater

- History of other malignancy within the last 5 years, except for carcinoma in situ of
the cervix or basal cell carcinoma

- Serious uncontrolled concomitant disease that would contraindicate the use of any of
the investigational drugs used in this study or would put the patients at high risk
for treatment -related complications

- Inadequate hematologic, liver or renal function

- Uncontrolled hypertension or clinically significant cardiovascular disease

- Hepatitis B, hepatitis C or HIV infection

- Current chronic daily treatment with corticosteroids (>/= 10 mg/day
methylprednisolone or equivalent), excluding inhaled steroids