Inclusion Criteria:

   - Histologically or cytologically confirmed and documented 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 v1.1 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 anti-cancer therapy in the metastatic or locally
   advanced breast cancer 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 (National Cancer Institute Common Terminology
   Criteria [NCI-CTC], Version 4.0) hematological toxicity resulting from previous
   adjuvant or neoadjuvant therapy

   - Radiographic evidence of central nervous system metastases that are not well
   controlled with local therapy (irradiation or surgery)

   - Current peripheral neuropathy of NCI-CTC, version 4.0 Grade 3 or greater

   - History of other malignancy within the last 5 years, except for carcinoma in situ of
   the cervix, non-melanoma skin carcinoma, Stage 1 uterine cancer, or cancers with a
   similar curative outcome as those mentioned above

   - Serious uncontrolled concomitant disease that would contraindicate the use of any of
   the investigational drugs used in this study or would put the participants 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 human immunodeficiency virus (HIV) infection

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