Letrozole in Preventing Breast Cancer in Postmenopausal Women

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