Lapatinib in Treating Patients With Advanced or Metastatic Breast Cancer That Overexpresses HER2

DISEASE CHARACTERISTICS:

Histologically confirmed breast cancer

Advanced or metastatic disease
No effective curative therapy available
Bone-only disease allowed

Tumor HER2 overexpression

HER2 3+ expression by immunohistochemistry OR > 2-fold (HER2 2+) gene amplification by fluorescence in situ hybridization

Evaluable disease

Measurable disease is not required
No progressive brain metastases
Hormone receptor status not specified

PATIENT CHARACTERISTICS:

Inclusion criteria:

ECOG performance status 0-2
Life expectancy > 3 months
Female
Menopausal status not specified
Absolute neutrophil count ≥ 1,000 cells/mm^3
Hemoglobin ≥ 9 g/dL
Platelet count ≥ 75,000 cells/mm^3
Total bilirubin normal
AST and ALT ≤ 3 x upper limits of normal (ULN) (≤ 5 x ULN with liver metastases)
Creatinine normal OR creatinine clearance ≥ 40 mL/min
INR ≤ 1.5
Potassium normal
Magnesium normal
Not pregnant
Negative pregnancy test
Fertile patients must use effective contraception prior to and during study therapy
Cardiac ejection fraction ≥ 50%

Consents to 2 tumor fine needle aspiration biopsies for biomarker analysis

Lung-only disease or sites otherwise deemed high-risk for biopsy, the requirement for biopsy will be waived

Exclusion criteria:

History of significant cardiac disease including any of the following:

Congestive heart failure
Symptomatic cardiac arrhythmias
Unstable angina
Uncontrolled prior lapatinib ditosylate therapy toxicity ≥ grade 2
Allergic reactions to IV contrast dye despite standard prophylaxis
History of malabsorption syndrome or disease significantly affecting gastrointestinal function or major resection of the stomach or small bowel that could affect absorption, distribution, metabolism, or excretion of study drug
Conditions that would impair the patient's ability to swallow and retain oral medication
Concurrent disease or condition that would make the patient inappropriate for study participation or would interfere with the patient's safety
Psychological, familial, sociological, or geographical conditions that do not permit compliance with the protocol

PRIOR CONCURRENT THERAPY:

Prior lapatinib ditosylate or trastuzumab allowed
At least 4 weeks since prior and no concurrent chemotherapy or investigational anticancer agents
At least 2 weeks since prior and no concurrent hormonal therapy
At least 2 weeks since prior and no concurrent lapatinib ditosylate prohibited medications, including CYP3A4 inhibitors or inducers, all herbal supplements, and gastric pH modifiers
More than 4 weeks since prior radiotherapy
No aspirin or plavix therapy within 7 days prior to tumor biopsy

No concurrent coumadin

Low molecular weight heparin allowed provided it can be held at least 24 hours prior to tumor biopsy
Concurrent gonadal suppression agents (i.e., Zoladex or Lupron) or palliative bisphosphonates (i.e., Zometa) allowed