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