Inclusion Criteria:

- Histologically confirmed adenocarcinoma of the breast with evidence of metastatic
disease

- Documented ErbB2 over expression or amplified disease in the invasive component of
the primary or metastatic lesion as defined by:

- ErbB2 gene amplification by FISH(>6 ErbB2 gene copies per nucleus, or a FISH ratio
(ErbB2 gene copies to chromosome 17 signals) of >than 2.2;

- Measurable disease, defined as ≥1 lesion that can be accurately measured in ≥1
dimension as ≥20 mm by conventional techniques OR as ≥10 mm by spiral CT scan

- In phase II part, patients must be chemo-naïve in metastatic setting.

- In phase I part, patient may have received prior chemotherapy in metastatic setting.

- In both phase I and II part, prior Anthracyclines allowed provided total dose of
doxorubicin hydrochloride ≤240 mg/m² or epirubicin ≤ 600 mg/m².

- At least 6 months since prior Anthracyclines, and 6 weeks since prior Taxane.

- Patient must be informed and well understand that in current standard of treatment,
suggested first line treatments for erbB-2 positive, visceral organ metastatic breast
cancer are combination of chemotherapy with herceptin.

- In phase II part, patient must not have exposed to ant-erbB2 targeted therapy
treatment in metastatic setting. Herceptin treatment in the neoadjuvant or adjuvant
setting is permitted provide that at least 12 months has elapsed since the last dose
of herceptin therapy.

- In phase I part, patient may have received prior anti-erbB-2 targeted treatment in
metastatic setting.

- Hormone receptor and menopausal status are not specified. Prior treatment with
endocrine therapy in the adjuvant or metastatic setting is permitted provided that
therapy be discontinued.

- Prior treatments with radiation therapy for palliative management of non-target
lesion metastatic disease is permitted provided that at least 2 weeks have elapsed
since the last fraction of radiation therapy, disease progression has been documented
and all treatment related adverse events are ≦ grade 1 at the time of registration.

- Life expectancy ≥ 12 weeks

- ECOG performance status 0-1

- Patients must have normal organ and marrow function measured within 14 days prior to
study entry as defined below:

- WBC ≥ 3,000/mm3

- Absolute neutrophil count ≥ 1,500/mm3

- Platelet count ≥ 100,000/mm3

- Bilirubin normal

- AST/ALT ≤ 2.5 times upper limit of normal

- Normal serum creatinine OR creatinine clearance ≥60 mL/min

- LVEF ≥ 50% (by MUGA)

- Negative pregnancy test

- Fertile patients must use effective contraception

- Able to swallow and retain medication

- No history of allergic reactions attributed to compounds of similar chemical or
biologic composition to lapatinib

- Patient consent must be obtained.

Exclusion Criteria:

- Pregnant or lactating women.

- Subjects who have current active hepatic or biliary disease (with exception of
patients with Gilbert's syndrome, asymptomatic gallstones, liver metastases or stable
chronic liver disease per investigator assessment)

- Prior therapy with concurrent use of Lapatinib.

- CNS metastasis.

- Ongoing other concurrent investigational agents or anticancer therapy

- Uncontrolled inter-current illness including, but not limited to, ongoing or active
infection, symptomatic congestive heart failure, uncontrolled hypertension, unstable
angina pectoris, cardiac arrhythmia, serious non-healing wound/ulcer/bone fracture,
or psychiatric illness/social situations that would limit compliance with study
requirements.

- Patients with GI tract disease resulting in an inability to take medication,
malabsorption syndrome, a requirement for IV alimentation, prior surgical procedures
affecting absorption, uncontrolled inflammatory GI disease (e.g., Crohn's, ulcerative
colitis).