What are phytoestrogens? do they cause or prevent breast cancer?

Plant compounds: Phytoestrogens are chemicals in plants that bind to the estrogen receptor (ER). They can stimulate or block the receptor. Soy beans and flax seeds contain phytoestrogens. Women in Asian countries who eat a lot of soy have a lower chance of getting breast cancer, so it may be preventive. But studies are conflicting. I tell my patients with ER+ breast cancer not to overdose on soy or flaxseed.