Tamoxifen in Preventing Breast Cancer in Women at Increased Risk for Breast Cancer

DISEASE CHARACTERISTICS: * At increased risk for breast cancer, as defined by 1 of the following criteria: * Histologically confirmed lobular carcinoma in situ (LCIS) treated by local excision only * Composite increased breast cancer risk of ≥ 1.67% over 5 years, based on the following criteria: * Age * Number of first-degree female relatives with breast cancer * One or more prior breast biopsies * Fine-needle aspiration cytology of a non-cystic lesion in lieu of an open biopsy is considered a biopsy * Prior diagnosis of atypical hyperplasia of the breast * Age at first live birth * Nulliparity * Race * Age at onset of menarche * No prior or suspected invasive breast cancer or ductal carcinoma in situ * No clinical evidence of malignancy by physical examination, including a breast examination within the past 3 months * No evidence of suspicious or malignant disease or uncharacterized lesions on bilateral mammogram within the past 6 months * Normal gynecologic examination, including a bimanual pelvic examination and, if indicated, pap smear within the past 12 months * Hormone receptor status: * Not specified PATIENT CHARACTERISTICS: Age * 35 and over Sex * Female Menopausal status * Premenopausal and ovulating\*, defined as having regular menses for the past 6 months OR irregular menses with follicular phase (i.e., day 3) follicle-stimulating hormone level \< 20 mIU/mL OR * Postmenopausal NOTE: \* Ovulation is determined by day 21 progesterone level \> 3 ng/mL Performance status * ECOG 0-2 Life expectancy * Not specified Hematopoietic * Complete blood count normal * No active bleeding disorder (e.g., qualitative or quantitative platelet abnormality, hemophilia, or von Willebrand's disease) Hepatic * Liver function tests normal Renal * Not specified Cardiovascular * No prior deep-vein thrombosis except a single occurrence related to lower extremity trauma * No prior cerebral vascular accident * No prior transient ischemic attack Pulmonary * No prior pulmonary embolus except a single occurrence related to lower extremity trauma Other * No saline or silicone breast implants * No known allergy to tamoxifen * No macular degeneration * No malignancy within the past 5 years except basal cell or squamous cell skin cancer or carcinoma in situ of the cervix * No nonmalignant disease that would preclude administration of tamoxifen * No psychiatric condition, including a history of clinical depression or addictive disorder, that would preclude giving informed consent or study compliance * Not pregnant or nursing * Negative pregnancy test * Fertile patients must use effective nonhormonal contraception during and for 3 months after study participation PRIOR CONCURRENT THERAPY: Biologic therapy * Not specified Chemotherapy * No prior systemic adjuvant chemotherapy for LCIS Endocrine therapy * No prior tamoxifen, raloxifene, or other selective estrogen-receptor modulators * At least 3 months since prior and no concurrent use of any of the following drugs: * Estrogen or progesterone replacement therapy * Oral contraceptives * Androgens * Luteinizing hormone-releasing hormone analogs * Prolactin inhibitors * Antiandrogens * Steroids * No concurrent steroids for asthma Radiotherapy * No prior radiotherapy for LCIS Surgery * No prior bilateral prophylactic mastectomy * No prior mastectomy for LCIS Other * Concurrent nonhormonal medications allowed * No concurrent warfarin or cholestyramine * No prior or concurrent participation in any other cancer prevention study * Patients treated with placebo on protocol NSABP-P-1 are eligible