I believe the 100% doesn't mean we have an excess amount of estrogen in our bodies. The 100% describes the cells the doctors analyzed. Of those cells they looked at under a microscope 100% of the cells were had receptors for estrogen, meaning they grow when they are fed estrogen. So I take Tamoxifen, which attaches to these cell receptors so the cancer cells can't grow. This is my elementary understanding at any rate!