GW572016 For Treatment Of Refractory Metastatic Breast Cancer

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.