The purpose of this study is to determine the efficacy of an oral investigational drug for the treatment of metastatic breast cancer tumors that are known to overexpress HER2/neu.

Inclusion Criteria: (The patient must meet the following criteria in order to be eligible for this study.)

• Signed informed consent
• No more than two prior regimens for metastatic breast cancer. Each regimen must have contained Herceptin.
• Refractory Stage IIIb or IV breast cancer
• HER2/neu tumor overexpression
• Disease progression while receiving a prior chemotherapy regimen with Herceptin alone or in combination with other chemotherapy.
• Tumor tissue available for testing.
• 2 weeks since treatment with Herceptin (alone or in combination).
• Able to swallow and retain oral medication
• Cardiac ejection fraction within the institutional range of normal as measured by MUGA (Multiple Gated Acquisition Scan).
• Adequate kidney and liver function
• Adequate bone marrow function

Exclusion Criteria: (The patient cannot meet any of the following criteria in order to be eligible for this study.)

• Prior regimens did not include Herceptin.
• Pregnant or lactating.
• Conditions that would affect absorption of an oral drug
• Serious medical or psychiatric disorder that would interfere with the patient's safety or informed consent.
• Severe cardiovascular disease or cardiac disease requiring a device.
• Active infection.
• Brain metastases.
• Concurrent cancer therapy or investigational therapy.
• Use of oral or IV steroids.
• Unresolved or unstable serious toxicity from prior therapy.
• Treatment with EGFR (Endothelial Growth Factor Receptor) inhibitor other than Herceptin.