Trastuzumab and Exemestane in Treating Postmenopausal Women With Metastatic or Locally Advanced Breast Cancer

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