4 Adding isoflavones back restores potency. Cancer Connection Asians also have lower breast and prostate cancer rates, perhaps due to soy isoflavones acting as phytoestrogens. Isoflavones could antagonize the action of estrogen, working as antiestrogens like the breast cancer drug tamoxifen in opposing tumor development. Some wonder whether isoflavones could actually stimulate estrogen receptors. In that case, they might promote cancer in some circumstances.
Breast tissue does respond to isoflavones with increased proliferation.
We simply don't know yet. Researchers think the stimulatory action of isoflavones actually works to women's advantage because the breast epithelial cells mature after they proliferate, thereby closing off cell cycling. If cells can't divide, they don't become cancerous. In other words, isoflavones early in life may prevent breast cancer later, especially if the first pregnancy also comes early, further pushing cells to mature. That explains why Asian women who ate soy before emigrating to the United States still have reduced breast cancer rates but their daughters raised on a Western diet do not.