Inclusion Criteria:

- Signed written and voluntary informed consent

- Histologically or cytologically confirmed breast cancer

- Stage IV (metastatic) breast cancer

- Biopsy (fresh or archival) of primary breast cancer or metastatic site demonstrating
HER2 gene amplification as determined in study-specified central laboratory by
fluorescence in situ hybridization (FISH)

- Prior treatment and progressive disease with at least 1 but not more than 2 cytotoxic
chemotherapy regimen(s) for metastatic disease

- Those for whom the use of an investigational HER2 inhibitor is appropriate because
they do not have access to approved HER2 inhibitors (e.g., Herceptin®) or for whom
treatment with currently available HER2 inhibitors is inappropriate

- Limited visceral disease burden (i.e., <30% involvement of any organ) and limited
disease-related symptoms (i.e., well controlled with supportive care measures)

- Presence of at least one measurable target lesion [i.e., malignant tumor mass that
can be accurately measured in at least 1 dimension of >=2 cm with conventional
radiographic techniques or magnetic resonance imaging, or >=1 cm with spiral CT scan
as per RECIST], excluding previously irradiated lesions, bone metastasis or pleural
effusion as sole manifestations of disease. If the measurable disease is restricted
to a solitary lesion, its neoplastic nature must be confirmed by cytology/histology

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

- Patient available for treatment, monitoring, and follow-up. Willing and able to
comply with scheduled visits, therapy plan, laboratory tests and blood sampling for
pharmacokinetic (PK) analyses

- Recovery to baseline or NCI CTCAE Version 3.0 Grade 1 toxicity from all acute effects
related to prior treatment, except alopecia

- Adequate Bone Marrow Function, including: a. Absolute neutrophil count (ANC) >=1500
cells/mm3; b. Platelets >=100,000 cells/mm3

- Adequate Renal Function, including: a. Estimated creatinine clearance >=60 mL/min; b.
SrCr <1.5 x ULN

- Adequate Liver Function, including: a. Bilirubin <=ULN (upper limit of normal); b.
AST (SGOT) <=2.5 x ULN; c. ALT (SGPT) <=2.5 x ULN

- Adequate Cardiac Function, including: a. 12-Lead electrocardiogram (ECG) with normal
tracing or non clinically significant changes that do not require medical
intervention; b. QTc interval <=450 msec and without history of Torsades des Pointes
or other symptomatic QTc abnormality; c. Left ventricular ejection fraction (LVEF) >=
institutional lower limit of normal and 45% as measured by echocardiogram or multi
gated radionuclide angiography (MUGA) within 4 weeks prior to start of study
treatment

- >= 18 years old

- Female

Exclusion Criteria:

- Women of child-bearing potential who are unwilling or unable to use an acceptable
method to avoid pregnancy for the entire study period and up to 4 weeks after study

- Women who are pregnant or breastfeeding

- Women with a positive pregnancy test on enrollment or within 72 hours prior to study
drug administration

- Prior treatment with trastuzumab (Herceptin®) or other HER2-targeting agents [e.g.,
lapatinib (GW572016), pertuzumab (Omnitarg™; rhuMab 2C4), CI 1033, EKB 569, CP
724,714]

- Cumulative dose >450 mg/m2 of doxorubicin or doxorubicin equivalents

- Prior high-dose chemotherapy requiring hematopoetic stem cell transplantation within
12 months of study treatment start

- Radiotherapy, investigational chemotherapy, biologic therapy within 4 weeks of study
treatment start

- Previous (within the last 5 years) or current malignancies arising from sites other
than breast, except for adequately treated basal cell or squamous cell skin cancer or
in situ carcinoma of the cervix uteri

- Known or clinically suspected brain metastasis or leptomeningeal disease (no
screening CT scan required) requiring therapy. Patients with asymptomatic previously
treated CNS metastases that no longer require therapy or
corticosteroids/anticonvulsants for at least 4 weeks prior to start of study
treatment are eligible

- Any clinically significant gastrointestinal abnormalities, which may impair intake,
transit or absorption of the study drug, such as the inability to take oral
medication in tablet form, prior complete/partial gastrectomy or intestinal
resection, or a requirement for H2 antagonists or proton pump inhibitors

- Any mental disorder that would limit the understanding or rendering of informed
consent and/or compromise compliance with the requirements of this protocol

- Uncontrolled or significant cardiovascular disease, including: a. Myocardial
infarction within 12 months; b. Uncontrolled angina within 6 months; c. Congestive
heart failure within 6 months or left ventricular ejection fraction below local
institutional lower limit of normal or below 45%; d. Diagnosed or suspected
congenital long QT syndrome; e. Any history of clinically significant ventricular
arrhythmias (such as ventricular tachycardia, ventricular fibrillation, or torsade de
pointes); f. Prolonged QTc interval on pre-entry electrocardiogram (>450 msec); g.
Any history of second or third degree heart block (may be eligible if currently have
a pacemaker); h. Heart rate <50/minute on pre-entry electrocardiogram; i.
Uncontrolled hypertension

- History of drug-induced hyperbilirubinemia

- Concurrent treatment with approved or investigational chemotherapy, hormonal therapy,
immunotherapy, or radiotherapy (hormone replacement therapy is permitted)

- Concurrent treatment with H2 antagonists and/or proton pump inhibitors. However, H2
antagonists can be used for the treatment of an unexpected hypersensitivity reaction
during the study period. Antacids are allowed but only up to 2 hours before and 2
hours after study drug administration

- Concurrent treatment or treatment within 4 weeks of first dose with potent and/or
irreversible CYP3A4 inhibitors including: ketoconazole, itraconazole, troleandomycin,
clarithromycin, erythromycin, ritonavir, indinavir, nelfinavir, saquinavir,
nefazodone, mibefradil, amiodarone and grapefruit juice

- Concurrent treatment or treatment within 4 weeks of first dose with potent inducers
of CYP3A4 including: rifampin, rifabutin, rifamycins, phenytoin, barbiturates,
carbamazepine, glucocorticoids, modafinil, phenobarbital, troglitazone, pioglitazone,
efavirenz, nevirapine, dexamethasone, and St. John's wort

- Prisoners or patients who are compulsorily detained or involuntarily incarcerated
(e.g., for treatment of infectious disease, psychiatric illness, etc.)