DISEASE CHARACTERISTICS:

• Histologically or cytologically confirmed HER2-overexpressing breast cancer

  • Prior or newly documented HER2 amplification by fluorescence in situ hybridization (FISH)
  • Progressive metastatic disease
• Must have received at least one prior chemotherapy regimen for metastatic breast cancer
• At least 1 measurable or evaluable lesion
• At least 1 lesion accessible for 2 separate core biopsies for pharmacodynamic evaluation
• No known or clinically suspected brain metastases or leptomeningeal disease
• No symptomatic edema or third-space fluid (e.g., ascites or pleural effusions)

• Hormone receptor status:

  • Not specified

PATIENT CHARACTERISTICS:

Age

• 18 and over

Sex

• Male or female

Menopausal status

• Not specified

Performance status

• ECOG 0-1

Life expectancy

• More than 3 months

Hematopoietic

• Absolute neutrophil count at least 1,500/mm^3*
• Platelet count at least 100,000/mm^3* NOTE: *Without hematopoietic growth factors or transfusions

Hepatic

• Bilirubin no greater than 1.5 mg/dL
• AST/ALT no greater than 2.5 times upper limit of normal (ULN) (5 times ULN if liver metastases are present)
• No known hepatitis B or C infection

Renal

• Creatinine no greater than 1.5 times ULN OR
• Creatinine clearance at least 60 mL/min

Cardiovascular

• 12-lead ECG with normal tracing

  • No significant ECG changes that require medical intervention

• QTc interval less than 460 msec

  • No history of torsade or other symptomatic QTc abnormality
• LVEF greater than 50% by MUGA
• No history of cardiovascular disease (i.e., ischemic heart disease, arrhythmia, or congestive heart failure) unless asymptomatic for the past year with no requirement for antiarrhythmics or a clinically significant medical management change

Gastrointestinal

• Able to take oral medication
• No gastrointestinal abnormality that would require medications (including all antacids)
• No persistent symptoms of an esophageal or digestive disorder

Other

• Not pregnant or nursing
• Negative pregnancy test
• Fertile patients must use effective contraception
• No known HIV infection
• No active infection
• No concurrent uncontrolled systemic disorders or laboratory abnormalities that would preclude study drug safety evaluation
• No mental disorder that would preclude study compliance or ability to give informed consent

PRIOR CONCURRENT THERAPY:

Biologic therapy

• See Chemotherapy

• At least 4 weeks since prior trastuzumab (Herceptin)

  • No more than 2 prior trastuzumab-based regimens for advanced disease
• At least 4 weeks since other prior biologic therapy or immunotherapy
• No concurrent immunotherapy

Chemotherapy

• See Disease Characteristics
• At least 4 weeks since prior chemotherapy (6 weeks for mitomycin or nitrosoureas)

• At least 6 months since prior doxorubicin or doxorubicin equivalents without any prior or developing signs or symptoms of cardiomyopathy

  • No cumulative doses of more than 300 mg/m^2
• No more than 1 prior anthracycline- or anthracenedione-containing regimen (except with approval of the sponsor)
• No prior high-dose chemotherapy with hematopoietic stem cell transplantation
• No concurrent anticancer chemotherapy

Endocrine therapy

• At least 2 weeks since prior hormonal therapy for the primary disease

  • Concurrent hormone replacement therapy or luteinizing hormone-releasing hormone agonists allowed
• No concurrent anticancer hormonal therapy, including tamoxifen

Radiotherapy

• At least 4 weeks since prior radiotherapy
• No prior radiotherapy to the only disease site that would be assessed for response
• No concurrent radiotherapy

Surgery

• At least 3 weeks since prior major surgery (2 weeks for minor surgery)
• No prior partial or complete gastrectomy

Other

• Recovered from prior therapy
• At least 4 weeks since prior investigational treatment
• No concurrent antiarrhythmics
• No concurrent antacids

• No concurrent anticoagulant at therapeutic doses

  • Coumarin or heparin derivatives allowed for the prevention of deep vein thrombosis or port patency
• No other concurrent experimental anticancer medications for breast cancer