Exemestane Compared With Tamoxifen in Treating Women With Locally Recurrent or Metastatic Breast Cancer

DISEASE CHARACTERISTICS: * Histologically or cytologically proven adenocarcinoma of the breast that is metastatic and progressive or locally recurrent and inoperable * At least one bidimensionally measurable or evaluable lesion * Lytic bone lesions on x-ray/CT scan, surrounded by calcified bone, and at least 1 cm * Bidimensionally measurable extraosseous disease required for patients on bisphosphonates * The following are not considered evaluable: * Previously irradiated lesions * Lymphangitic spread * Ascites * Blastic bone lesions * Pleural effusions * No rapidly progressive disease for which hormonal therapy is not indicated * No massive visceral disease (i.e., more than one third of any organ) * No brain metastases * Hormone receptor status: * Estrogen receptor positive or progesterone receptor positive, defined by 1 of the following: * At least 10 femtomoles H3-estrogen or at least 20 femtomoles * H3 progesterone binding per mg of cytosol protein by DCC or sucrose density method * At least 0.10 femtomoles H3-estrogen or at least 0.20 femtomoles * H3-progesterone binding per mg of DNA by IF/EIA technique * Positive immunohistochemistry noted on pathology report * Unknown receptor status eligible provided: * Disease-free interval of at least 2 years since adjuvant therapy or initial surgery (if no adjuvant therapy), including most recently treated tumor in bilateral breast cancer if status unknown in one primary tumor PATIENT CHARACTERISTICS: Age: * 18 and over Sex: * Female Menopausal status: * Postmenopausal by 1 of the following: * Natural menopause and more than 1 year since last menstrual period (LMP) * Radiation-induced oophorectomy and more than 1 year since LMP * Chemotherapy induced menopause if: * At least 1 year since LMP (+ 1 year post-tamoxifen) * Serum FSH and LH and plasma estradiol levels in postmenopausal range * LHRH-induced amenorrhea * Surgical castration * Patients under age 56 with prior hysterectomy and 1 or both ovaries intact or tamoxifen-induced amenorrhea with at least 12 months since prior tamoxifen must have postmenopausal serum FSH and LH and plasma estradiol concentrations Performance status: * ECOG (WHO) 0-2 Hematopoietic: * Absolute neutrophil count at least 1,500/mm\^3 * Platelet count at least 100,000/mm\^3 Hepatic: * Bilirubin less than 1.5 times upper limit of normal (ULN) * SGOT/SGPT less than 2.5 times ULN (less than 5 times ULN with liver metastases) Renal: * Creatinine less than 1.5 times ULN Cardiovascular: * No deep venous thrombosis Other: * No mental incapacitation * No severe concurrent disease * No prior or concurrent malignancy except curatively treated carcinoma in situ of the cervix or basal cell or squamous cell skin cancer PRIOR CONCURRENT THERAPY: Biologic therapy: * No concurrent immunotherapy Chemotherapy: * See Disease Characteristics * At least 3 weeks since chemotherapy for metastatic disease and recovered * No more than 1 prior chemotherapy regimen for metastatic disease * Prior adjuvant chemotherapy allowed if disease free for at least 6 months * No concurrent chemotherapy Endocrine therapy: * No prior hormonal therapy for advanced disease (e.g., tamoxifen or LHRH agonists) * Prior adjuvant tamoxifen allowed if disease free for at least 6 months * No other concurrent hormonal therapy, including steroids Radiotherapy: * Recovered from toxic effects of prior radiotherapy * Concurrent palliative radiotherapy, including whole brain irradiation, allowed Surgery: * See Disease Characteristics * No prior ovariectomy for advanced disease Other: * No other concurrent investigational drugs * Concurrent bisphosphonates allowed if short term (7 days) for hypercalcemia due to suspect tumor flare or if on prior bisphosphonates with bidimensionally measurable extraosseous lesion