Inclusion Criteria

DISEASE CHARACTERISTICS:

- Histologically confirmed breast cancer

- Stage IV or locally advanced disease

- Staged by bone scan or CT scan of chest and/or abdomen within the past 6
weeks

- HER2/neu positive by fluorescent in situ hybridization (if 2+ by
immunohistochemistry) or 3+ by immunohistochemistry

- Measurable disease defined by 1 of the following criteria:

- At least 1 dimension at least 1 cm by CT scan or other imaging scan

- At least 1 diameter at least 1 cm by plain x-ray (excluding bone lesions)

- Palpable lesion with both diameters at least 1 cm with caliper OR

- Evaluable disease defined by 1 of the following criteria:

- Positive bone scan

- Palpable masses with diameter less than 1 cm, masses with margins not clearly
defined on CT scan or x-ray, or with both diameters less than 1 cm

- Bone scan and CA 27.29 if bone scan only evaluable disease

- Hormone receptor status:

- Estrogen receptor and/or progesterone receptor positive

PATIENT CHARACTERISTICS:

Age

- 18 and over

Sex

- Female

Menopausal status

- Postmenopausal by 1 of the following criteria:

- 60 years of age and over

- 45 years of age and over with amenorrhea more than 12 months and an intact
uterus

- Follicle-stimulating hormone levels within postmenopausal range

- Undergone bilateral oophorectomy

Performance status

- ECOG 0-2

Life expectancy

- Not specified

Hematopoietic

- Not specified

Hepatic

- Bilirubin less than 1.5 times upper limit of normal

Renal

- Creatinine less than 2 mg/dL

Cardiovascular

- Ejection fraction greater than 50%

Other

- Not pregnant or nursing

PRIOR CONCURRENT THERAPY:

Biologic therapy

- No prior trastuzumab (Herceptin)

Chemotherapy

- Prior chemotherapy allowed

Endocrine therapy

- No prior exemestane

- No other prior hormonal agent (except tamoxifen)

Radiotherapy

- Not specified

Surgery

- Not specified