Acolbifene Versus Low Dose Tamoxifen for the Prevention of Breast Cancer in Premenopausal Women at High Risk for Development of Breast Cancer

Inclusion Criteria: * Age \>= 35 years * Considered clinically premenopausal * Having regular menstrual cycles (between 21 and 35 days) unless a contraceptive device such as progestin containing intrauterine device (IUD) (e.g., Mirena IUD) is being used which suppresses menstrual periods, or premenopausal women who have undergone a hysterectomy, but ovaries are intact * Not considering pregnancy for at least 12 months * Women of child-bearing potential capacity must be willing to have used effective birth control precautions for 8 weeks prior to fine needle aspiration and be willing to continue for 8 weeks after study completion as tamoxifen may have teratogenic effects on the developing fetus. Reproductive and developmental toxicity studies have not been conducted with acolbifene. Should a woman become pregnant or suspect she is pregnant while participating in this study, she must stop study drug and inform her study physician immediately. * For women not using oral contraceptive (progestin alone or estrogen plus a progestin), two of the following are recommended but woman must agree to at least one of the following methods: * IUD non-hormonal or hormone containing (usually a progestin) intrauterine device (IUD) or rings. Any of these should have been inserted at least 8 weeks prior to RPFNA. * Barrier method (such as condoms and diaphragms or cervical caps with or without a spermicide) * Partner has had a vasectomy. * For women using oral contraceptive (p…