Inclusion Criteria

DISEASE CHARACTERISTICS:

Phase I:

- Histologically confirmed infiltrating ductal carcinoma of the breast

- Metastatic disease

- Clinically asymptomatic with non-life-threatening metastases allowed

- Measurable or evaluable disease by radiograph, CT scan, MRI, nuclear medicine bone
scan, or physical examination

- No measurable disease allowed if tumor or metastasis has been removed or
successfully treated prior to study

- No rapidly progressive symptomatic disease affecting major organ systems (e.g., lungs
and liver)

- Stable or unstable disease for 3 months on hormonal therapy

- Stable or unstable disease for at least 1 month after chemotherapy

- No active brain metastases

- Brain metastases previously treated with definitive radiotherapy and/or surgical
resection allowed

- Hormone receptor status:

- Estrogen and progesterone receptor status known

Phase II:

- All Phase I criteria

- HER2/neu overexpression (2+ or 3+) by immunohistochemistry

- Prior trastuzumab (Herceptin) allowed if disease still overexpresses HER2/neu

PATIENT CHARACTERISTICS:

Age:

- 18 and over

Sex:

- Female

Menopausal status:

- Not specified

Performance status:

- Karnofsky 70-100% OR

- ECOG 0-2

Life expectancy:

- At least 3 months

Hematopoietic:

- Granulocyte count at least 1,500/mm^3

- Platelet count at least 50,000/mm^3

- Hemoglobin at least 8 g/dL

Hepatic:

- Bilirubin less than 1.5 times normal

- SGOT less than 1.5 times normal

Renal:

- Creatinine no greater than 1.8 mg/dL

- Creatinine clearance at least 60 mL/min

- BUN no greater than 1.5 times normal

Cardiovascular:

- No myocardial infarction within the past year

- No prior myocardial infarction with coronary symptoms requiring medication and/or
depressed left ventricular function (LVEF less than 50% by MUGA)

- No angina or coronary symptoms requiring medication and/or with depressed left
ventricular function (LVEF less than 50% by MUGA)

- No congestive heart failure requiring medical management

- LVEF at least 50% at rest by MUGA

- No uncontrolled hypertension (i.e., systolic blood pressure [BP] ≥ 130 mm Hg or
diastolic BP ≥ 80 mm Hg)

Pulmonary:

- FEV1, DLCO, and FVC at least 50% predicted

Other:

- Not pregnant or nursing

- Negative pregnancy test

- Fertile patients must use effective contraception

- HIV negative

- No other serious medical or psychiatric illness that would preclude study
participation

- No other prior or concurrent malignancy within the past 5 years except curatively
treated squamous cell carcinoma in situ of the cervix, basal cell skin cancer, or any
other curatively treated disease in complete remission

PRIOR CONCURRENT THERAPY:

Biologic therapy:

- See Disease Characteristics

- Prior trastuzumab allowed for phase I

Chemotherapy:

- See Disease Characteristics

- At least 4 weeks since prior chemotherapy

Endocrine therapy:

- See Disease Characteristics

- Concurrent hormonal therapy for breast cancer must continue during study

- No other concurrent hormonal therapy except steroids for adrenal failure, septic
shock, or pulmonary toxicity or hormonal therapy for non-disease-related conditions
(e.g., insulin for diabetes)

Radiotherapy:

- See Disease Characteristics

Surgery:

- See Disease Characteristics