Statement: Candidates for the primary trial must have a bone density scan 1 month prior to study entry, if the results from this are more than 2 standard deviations below normal, they must be excluded.
Primary_evidence: DISEASE CHARACTERISTICS:   At increased risk for the development or recurrence of breast cancer, defined as an estradiol level  9 pg/mL   No evidence of suspicious or malignant disease, based on the following examinations:   Clinical bilateral breast examination within the past 6 months   Bilateral* mammogram within 3 months before randomization OR within 30 days after randomization   Pelvic exam normal within the past 5 years   General physical exam within the past 6 months NOTE: *Unilateral mammogram of the uninvolved breast for patients with prior invasive breast cancer or ductal carcinoma in situ (DCIS)   Bone density scan within 2 standard deviations from normal within the past 30 days   Bone density scan  2 standard deviations below normal allowed if approved by the study physician   At least 1 breast that has not been previously treated with radiotherapy or surgery (for patients with prior invasive breast cancer or DCIS)   Hormone receptor status:   Not specified   PATIENT CHARACTERISTICS:   Age   35 and over   Sex   Female   Menopausal status   Postmenopausal, defined by any of the following criteria:   At least 12 months without spontaneous menstrual bleeding   Prior hysterectomy and bilateral salpingo-oophorectomy    55 years of age with a prior hysterectomy with or without oophorectomy   < 55 years of age with a prior hysterectomy without oophorectomy OR the status of the ovaries is unknown AND follicle-stimulating hormone (FSH) level is in the postmenopausal range   Performance status   Normal activity must not be restricted for a significant portion of the day   Life expectancy   At least 10 years   Hematopoietic   Complete blood count with differential normal   Prior benign neutropenia allowed provided the granulocyte count is  1,500/mm^3   Hepatic   Bilirubin normal   Alkaline phosphatase normal   SGOT and SGPT normal   Renal   Creatinine normal   Cardiovascular   No uncontrolled cardiovascular disease   Other   Not pregnant   No other malignancy within the past 5 years except basal cell or squamous cell skin cancer or carcinoma in situ of the cervix   No osteoporosis   No hyperlipidemia   No mental health status resulting in cognitive or emotional impairment that would preclude study participation   PRIOR CONCURRENT THERAPY:   Biologic therapy   Not specified   Chemotherapy   Not specified   Endocrine therapy   More than 30 days since prior AND no concurrent use of any of the following hormonal agents:   Estrogen or progesterone replacement therapy   Oral contraceptives   Raloxifene or other plasma estrogen receptor modulators (SERMs)   Androgens (e.g., danazol)   Luteinizing hormone-releasing hormone (LHRH) analogs (e.g., goserelin or leuprolide)   Prolactin inhibitors (e.g., bromocriptine)   Antiandrogens (e.g., cyproterone)   More than 60 days since prior AND no concurrent tamoxifen   No prior aromatase inhibitors (for patients with prior invasive breast cancer or DCIS)   No concurrent phytoestrogenic dietary supplements (e.g., soy, ginseng, or other natural products)   Dietary soy allowed   Radiotherapy   See Disease Characteristics   Surgery   See Disease Characteristics   No prior bilateral mastectomy   Other   More than 60 days since prior treatment for invasive breast cancer or DCIS   More than 30 days since prior bisphosphonates or calcitonin   No prior or concurrent participation on a treatment study for invasive breast cancer or DCIS   No concurrent participation in any other cancer prevention study or osteoporosis prevention study involving pharmacologic agents   No concurrent calcitonin   No concurrent bisphosphonate therapy   Concurrent cholecalciferol (vitamin D) and calcium to augment bone mineral density allowed