Inclusion Criteria

DISEASE CHARACTERISTICS:

- Histologically or cytologically confirmed breast cancer

- Advanced disease

- Measurable disease, defined as ≥ 1 unidimensionally measurable lesion outside
previously irradiated areas that is ≥ 20 mm OR ≥ 10 mm if the slice thickness of the
CT scan or MRI is ≤ 5 mm

- No nonmeasurable lesions as the only site of measurable disease, including any
of the following:

- Osteoblastic bone metastases

- Ascites

- Pleural or pericardial effusions

- Carcinomatous lymphangitis of the lung

- Progressive disease after prior treatment with a nonsteroidal aromatase inhibitor
(e.g., letrozole or anastrozole) in an adjuvant or advanced disease setting

- HER-2 amplification ≥ 2 by fluorescence in situ hybridization

- No clinical symptoms or history of CNS or leptomeningeal metastases (no imaging is
required)

- No visceral involvement with risk for organ dysfunction

- Hormone receptor status:

- Estrogen receptor- and/or progesterone receptor-positive tumor

PATIENT CHARACTERISTICS:

Age

- 18 and over

Sex

- Female

Menopausal status

- Postmenopausal, defined by 1 of the following:

- At least 55 years of age

- Less than 55 years of age with spontaneous cessation of menses for ≥ 1 year

- Less than 55 years of age with spontaneous cessation of menses within the past
year, but amenorrheic with biochemical evidence of postmenopausal status

- Underwent prior bilateral oophorectomy

- Radiation or chemically induced menopause (treatment with luteinizing
hormone-releasing hormone antagonists must continue during study treatment)

Performance status

- WHO 0-1

Life expectancy

- Not specified

Hematopoietic

- WBC ≥ 3,000/mm^3

- Platelet count ≥ 100,000/mm^3

Hepatic

- AST and ALT ≤ 2 times upper limit of normal

Renal

- Creatinine clearance > 30 mL/min

Cardiovascular

- No uncontrolled cardiac disease, including any of the following:

- Unstable angina

- Arrhythmia

- Hypertension

- No history of congestive heart failure

- No myocardial infarction within the past 6 months

- LVEF > 50% by echocardiogram

Pulmonary

- No severe dyspnea at rest

Other

- No other malignancy within the past 5 years except adequately treated carcinoma in
situ of the cervix or localized nonmelanoma skin cancer

- No psychiatric disability that would preclude study participation or giving informed
consent

- No active autoimmune disease

- No uncontrolled diabetes

- No other serious underlying medical condition that would preclude study participation

PRIOR CONCURRENT THERAPY:

Biologic therapy

- No prior trastuzumab (Herceptin®)

Chemotherapy

- Prior neoadjuvant or adjuvant chemotherapy allowed

- No prior palliative chemotherapy

Endocrine therapy

- See Disease Characteristics

Radiotherapy

- See Disease Characteristics

Surgery

- Not specified

Other

- More than 1 month since prior experimental drugs on another clinical trial

- No concurrent drugs that contraindicate study treatment

- No other concurrent anticancer drugs

- No other concurrent investigational drugs