DISEASE CHARACTERISTICS:

Histologically confirmed breast cancer, meeting one of the following criteria:

Locally advanced disease (i.e., stage IIIB or IIIC [T4 primary tumor] disease)
Metastatic disease
Disease progressed after treatment with regimens that included trastuzumab (Herceptin®) in combination with an anthracycline and/or a taxane

Must have received 1-2 prior chemotherapy regimens in the neoadjuvant, adjuvant, or metastatic setting

One regimen must have included treatment with an anthracycline and/or a taxane
Prior treatment with trastuzumab required unless there is a contraindication for trastuzumab treatment
HER2-positive disease, defined by any of the following:

Validated IHC assay score of 3+ (defined as uniform, intense staining of > 30% of invasive tumor cells)
Average HER2 gene copy number > 6
Gene amplified (HER2:D17Z1 ratio > 2.20)
Measurable disease according to RECIST criteria
No evidence of active brain metastases, including leptomeningeal involvement

CNS metastasis controlled* by prior surgery and/or radiotherapy is allowed NOTE: *To be considered controlled, there must have been no symptoms for at least 2 months or no evidence of progression prior to study entry AND corticosteroid therapy must have been discontinued
Hormone receptor status not specified
PATIENT CHARACTERISTICS:

Menopausal status not specified
ECOG performance status 0-2
Life expectancy > 3 months
WBC = 3,000/mm³
ANC = 1,500/mm³
Platelet count = 75,000/mm³
Hemoglobin > 9.0 g/dL
Total bilirubin = 1.5 times upper limit of normal (ULN)
AST and ALT = 2.5 times ULN (5 times ULN if elevations are due to liver metastases)
Serum creatinine = 1.5 times ULN
Creatinine clearance = 30 mL/min
Fasting glucose < 120 mg/dL

Diabetes allowed provided blood glucose level meets the above criterion
INR = 1.5 times ULN
LVEF = 50% by MUGA or ECHO
Not pregnant or nursing
Negative pregnancy test
Fertile patients must use effective contraception
Willing to provide tissue and blood samples for research purposes
Able to complete questionnaires by self or with assistance
No other stage III or IV invasive cancer within the past 5 years
No other malignancy requiring active treatment, except nonmelanoma skin cancer or carcinoma in situ of the cervix

History of prior malignancy allowed provided patient is not receiving other specific treatment for their malignancy
No current, active hepatic or biliary disease, except Gilbert syndrome's or asymptomatic gallstones
No New York Heart Association class III or IV cardiovascular disease
No concurrent uncontrolled illness including, but not limited to, any of the following:

Poorly controlled diabetes
Ongoing or active infection
Symptomatic congestive heart failure
Unstable angina pectoris
Cardiac arrhythmia
Psychiatric illness/social situation that would preclude compliance with study requirements
No co-morbid systemic illness or other severe concurrent disease that, in the judgment of the investigator, would make the patient inappropriate for entry into this study or interfere significantly with the proper assessment of the safety of the prescribed study regimens
Not immunocompromised (other than that related to the use of corticosteroids), including known HIV-positivity with an AIDS-defining illness

HIV-positive patients with a CD4 count within normal range and who have no history of an AIDS-defining illness are eligible
PRIOR CONCURRENT THERAPY:

See Disease Characteristics
Prior hormonal therapy in the neoadjuvant, adjuvant, or metastatic setting allowed
More than 6 weeks since prior major surgery, chemotherapy, or immunologic therapy
More than 4 weeks since prior radiotherapy, except a single dose of palliative radiotherapy or radiotherapy to a non-target lesion

Prior radiotherapy to a target lesion is allowed only if there has been clear progression of the lesion since completion of radiotherapy
Recovered from prior radiotherapy
No more than 2 prior chemotherapy regimens for metastatic d