An Open-Label, Multicenter, Single Arm Phase II Study of Oral GW572016 as Single Agent Therapy in Subjects With Advanced or Metastatic Breast Cancer Who Have Progressed While Receiving HERCEPTIN-Containing Regimens

Inclusion Criteria:

- Signed Informed Consent.

- Histologically confirmed Stage IIIb or IV breast cancer.

- Refractory breast cancer defined as progression in the metastatic setting after prior
therapy with anthracyclines, taxanes and capecitibine.

- Subjects with documented ErbB2 tumor overexpression must have received at least 6
cycles of trastuzumab.

- Documented disease progression of the most recent treatment is required.

- Archived tumor tissue available for testing.

- Measurable lesions according to Response Evaluation Criteria In Solid Tumors
(RECIST).

- At least 3 weeks since prior cancer therapies except for trastuzumab which must be
discontinued at least 2 weeks prior to the beginning of study drug.

- Bisphosphonate therapy initiated prior to study entry is allowed, however, initiation
of bisphosphonates following study entry is not allowed.

- Able to swallow and retain oral medication.

- Cardiac ejection fraction within the institutional normal range as measured by
echocardiogram or MUGA (Multiple Gated Acquisition) scan.

- Adequate kidney and liver function.

- Adequate bone marrow function.

Exclusion criteria:

- Pregnant or lactating.

- Copies of nadir scans and/or photographs of the tumor prior to disease progression as
well as scans documenting disease progression are not available for review.

- Malabsorption syndrome, ulcerative colitis, disease significantly affecting
gastrointestinal function or resection of the stomach or small bowel.

- History of other malignancy.

- Serious medical or psychiatric disorder that would interfere with the patient''s
safety or informed consent.

- Active or uncontrolled infection.

- Known history of uncontrolled or symptomatic angina, arrhythmias or congestive heart
failure.

- Known history of or clinical evidence of leptomeningeal carcinomatosis.

- Active infection.

- Concurrent cancer therapy or investigational therapy.

- Use of oral or IV steroids.

- Unresolved or unstable serious toxicity from prior therapy.

- Prior treatment with an ErbB1 and/or ERbB2 inhibitor other than trastuzumab.