Inclusion Criteria

DISEASE CHARACTERISTICS:

- Histologically confirmed metastatic breast cancer c-erbB2 positive (3+ overexpression
by the HercepTest™ method) in the primary tumor or metastatic site

- At least 1 unidimensionally measurable target lesion

- At least 20 mm by conventional techniques OR

- At least 10 mm by spiral CT scan

- Lesions that have been irradiated in the preceding 3 months cannot be used as
target lesions unless they have appeared or clearly progressed since prior
irradiation

- No bone lesions as the only target lesions

- No contralateral breast cancer that is c-erbB2-positive or c-erbB2-negative/unknown,
with status determined on a metastatic site

- No CNS metastases

- CT scan of brain and CSF cytology are required if neurologic symptoms are
present

- Hormone receptor status:

- Any estrogen or progesterone receptor status

PATIENT CHARACTERISTICS:

Age:

- 18 and over

Sex:

- Female

Menopausal status:

- Any status

Performance status:

- ECOG 0-2

Life expectancy:

- Not specified

Hematopoietic:

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

- Platelet count at least 100,000/mm^3

Hepatic:

- Bilirubin no greater than 1.25 times upper limit of normal (ULN)

- Transaminases less than 2.5 times ULN (5 times ULN if liver metastases present)

Renal:

- For patients age 18 to 69:

- Creatinine no greater than ULN

- For patients age 70 and over:

- Creatinine clearance normal

Cardiovascular:

- LVEF normal by MUGA or echocardiogram

- No clinical heart failure

Pulmonary:

- No malignancy-associated dyspnea at rest

- No requirement for supportive oxygen therapy

Other:

- Not pregnant or nursing

- No other prior or concurrent malignancy within the past 5 years except adequately
treated carcinoma in situ of the cervix or basal cell skin cancer

- No psychological, familial, sociological, or geographical condition that would
preclude compliance with study therapy and follow-up schedule

PRIOR CONCURRENT THERAPY:

Biologic therapy:

- No prior anti-c-erbB2 antibody, including trastuzumab (Herceptin®)

- No other concurrent biologic therapy

Chemotherapy:

- No more than 1 prior chemotherapy regimen for metastatic breast cancer

- Prior combination of cyclophosphamide, methotrexate, and fluorouracil (CMF) allowed
in the adjuvant or metastatic setting only if the disease-free interval after
completion of CMF was at least 12 months

- Prior anthracyclines and/or taxanes allowed

- At least 4 weeks since prior anthracyclines

- No prior cumulative dose of doxorubicin more than 360 mg/m^2

- No prior cumulative dose of epirubicin more than 720 mg/m^2

- No prior cumulative dose of mitoxantrone more than 90 mg/m^2

- No other concurrent chemotherapy

Endocrine therapy:

- More than 2 weeks since prior hormonal therapy in the adjuvant or metastatic setting

- No concurrent hormonal therapy

Radiotherapy:

- See Disease Characteristics

- No concurrent radiotherapy

Surgery:

- Not specified

Other:

- No other concurrent anticancer therapy or investigational drugs

- No concurrent bisphosphonates started after study enrollment except for hypercalcemia