Inclusion Criteria:

- Signed study-specific Informed Consent Form(s)

- Age ≥ 18 years

- Histologically documented breast cancer

- HER2-positive disease

- Metastatic breast cancer

- Disease progression on the last chemotherapy regimen received in the metastatic
setting

- Prior treatment with an anthracycline, trastuzumab, a taxane, lapatinib, and
capecitabine in the neoadjuvant, adjuvant, locally advanced, or metastatic setting
and prior treatment with at least two lines of therapy (a line of therapy can be a
combination of two agents or single-agent chemotherapy) in the metastatic setting

- At least two lines of anti-HER2 therapy must have been given in the metastatic
setting as monotherapy or combined with chemotherapy or hormonal therapy. The
HER2-targeted agent can include trastuzumab, lapatinib, or an investigational agent
with HER2-inhibitory activity.

- A minimum of 6 weeks of trastuzumab for the treatment of metastatic disease is
required

- Patients must have had at least 14 days of exposure in the metastatic setting to
lapatinib and capecitabine (given together or separately) unless they were intolerant
of lapatinib and/or capecitabine

Exclusion Criteria:

- Chemotherapy ≤ 21 days before enrollment

- Trastuzumab ≤ 21 days before enrollment

- Hormone therapy ≤ 7 days before enrollment

- Granulocyte-stimulating agent < 14 days before enrollment

- Investigational therapy ≤ 28 days before enrollment

- Previous radiotherapy for treatment of metastatic breast cancer ≤ 21 days before
enrollment

- Brain metastases that are untreated, symptomatic, or require therapy to control
symptoms; or any radiation, surgery, or other therapy to control symptoms from brain
metastases within 3 months of the first study treatment

- History of intolerance (including Grade 3-4 infusion reaction) or hypersensitivity to
trastuzumab or murine proteins

- History of exposure to the following cumulative doses of anthracyclines: Doxorubicin
or liposomal doxorubicin > 500 mg/m^2; Epirubicin > 900 mg/m^2; Mitoxantrone > 120
mg/m^2 and idarubicin > 90 mg/m^2

- Peripheral neuropathy of Grade ≥ 3 per National Cancer Institute Common Terminology
Criteria for Adverse Events (NCI CTCAE), v3.0

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

- Current unstable angina

- History of symptomatic congestive heart failure (CHF), or ventricular arrhythmia
requiring treatment

- History of myocardial infarction within 6 months of enrollment

- Left ventricular ejection fraction (LVEF) < 50% within 28 days of enrollment

- History of decreased LVEF to < 50% or symptomatic CHF with previous adjuvant
trastuzumab treatment

- Severe dyspnea at rest due to complications of advanced malignancy or requiring
current continuous oxygen therapy

- Current severe, uncontrolled systemic disease (e.g., clinically significant
cardiovascular, pulmonary, or metabolic disease)

- Major surgical procedure or significant traumatic injury within 28 days before
enrollment or anticipation of the need for major surgery during the course of study
treatment

- Current pregnancy or lactation

- Current known infection with human immunodeficiency virus (HIV), active hepatitis B,
and/or hepatitis C virus

- Assessed by the investigator to be unable or unwilling to comply with the
requirements of the protocol