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