Bio-identical progesterone (including FDA approved Prometrium) has not been shown to increase the risk of breast cancer like the synthetic progestins. In addition, progesterone, used vaginally, does not negate the beneficial effects of estrogen on the heart like the synthetic progestins. Estriol is a bio-identical estrogen widely used in Europe that does not bind strongly to estrogen receptor and does not stimulate breast tissue. Numerous studies have shown that vaginal estriol does not increase the risk of breast cancer. It has safely been used in breast cancer survivors. However, higher doses of vaginal estradiol (> 25 mcg) and vaginal Premarin provide systemic levels of strong estrogens that may stimulate breast tissue. If you are a breast cancer survivor, it is important that you understand this. Balanced hormones are the key to health and disease prevention.