International Breast Cancer Intervention Study

DISEASE CHARACTERISTICS: * Meets at least 1 of the relative risk factors based on age as follows: * 45 to 70 years of age: * First-degree relative who developed breast cancer at ≤ 50 years of age * First-degree relative who developed bilateral breast cancer * Two or more first- or second-degree relatives who developed breast cancer or ovarian cancer * Participants having both relatives who are second degree and on the opposite sides of the family must have at least one that was diagnosed at ≤ 50 years of age * Nulliparous (or first birth at ≥ 30 years of age) and a first-degree relative who developed breast cancer * Benign biopsy with proliferative disease and a first-degree relative who developed breast cancer * Mammographic opacity covering at least 50% of the breast in the absence of hormone replacement therapy within the past 3 months * 60 to 70 years of age: * First-degree relative with breast cancer at any age * Age at menopause ≥ 55 years * Nulliparous or age at first birth ≥ 30 years * 40 to 44 years of age: * Two or more first- or second-degree relatives who developed breast cancer or ovarian cancer at ≤ 50 years of age * First-degree relative with bilateral breast cancer who developed the first breast cancer at ≤ 50 years of age * Nulliparous (or first birth at ≥ 30 years of age) and a first-degree relative who developed breast cancer at ≤ 40 years of age * Benign biopsy with proliferative disease and a first-degree relative who developed breast cancer at ≤ 40 years of age * All age groups (40 to 70 ears of age) with a 10-year risk \> 5% who do not fit into the above categories are allowed * Clearly apparent family history AND/OR other risk factors indicating appropriate increased risk of breast cancer for age * The following prior breast conditions are allowed (for all age groups): * Lobular carcinoma in situ * Atypical ductal or lobular hyperplasia in a benign lesion * Ductal carcinoma in-situ (DCIS), diagnosed within the past 6 months, and treated by mastectomy * No evidence of breast cancer on mammogram within the past year * Hormone receptor status: * For patients with prior DCIS, estrogen- or progesterone-receptor status must have been positive * Must have had greater than or equal to 5% positive cells PATIENT CHARACTERISTICS: Age * 40 to 70 Sex * Female Menopausal status * Postmenopausal, defined as at least 1 of the following: * Over 60 years of age * Bilateral oophorectomy * ≤ 60 years of age with a uterus and amenorrhea for at least 12 months * ≤ 60 years of age without a uterus and with follicle-stimulating hormone levels \> 30 IU/L Performance status * Not specified Life expectancy * At least 10 years Hematopoietic * Not specified Hepatic * Not specified Renal * Not specified Other * Psychologically and physically suitable to receive 5 years of anti-estrogen therapy * No cancer within the past 5 years except non-melanoma skin cancer or carcinoma in situ of the cervix * No evidence of osteoporosis or fragility fractures within the spine * Participants with a T-score \> minus 4 and no more than 2 fragility fractures are allowed * No concurrent severe disease that would place the participant at unusual risk or confound the results of the study * No other medical condition that would preclude the ability to receive the study treatment PRIOR CONCURRENT THERAPY: Biologic therapy * Not specified Chemotherapy * Not specified Endocrine therapy * No prior tamoxifen, raloxifene, or other selective estrogen receptor modulator (SERM) use for more than 6 months in duration unless an IBIS-I participant (must have been off trial therapy for at least 5 years. * No concurrent tamoxifen, raloxifene, or other SERM * No concurrent estrogen-based hormone replacement therapy * No concurrent systemic estrogen replacement therapy, including vaginal estrogen preparations Radiotherapy * Not specified Surgery * See Disease Characteristics * No prior prophylactic mastectomy * No concurrent prophylactic mastectomy Other * More than 6 months since prior investigational drugs