Black Cohosh and breast cancer

The root of this woodland plant is back in the forefront in a new study from the University of Pennsylvania that tracks its use, among other herbals, in perimenopausal women who also had breast cancer (over 900) along with controls (over 1500). Not only do we continue to see improvement in menopausal symptoms, but Black Cohosh specifically seems to protect against breast cancer.
There has long been a debate as to whether "phytoestrogens" (mostly steroidal-like molecules present in plants) are harmful or helpful in cases of breast cancer. The argument that plants like Black Cohosh are harmful runs something like this: if estrogen-dependent breast cancers are exposed to estrogen-like substances from the plant world, proliferation will ensue as these substances are mild agonists at the estrogen receptor - after all, they help alleviate estrogen-deficiency symptoms, right? In contrast, many herbalists argue that phytoestrogens are amphoteric, and their weak action at the estrogen receptor actually leads to less proliferation by blocking the receptor from the much more powerful human estrogen. Since cancer cells are overproducing this receptor, Black Cohosh actually has a net benefit by "plugging up" those cancer-stimulating sites.
Hopefully this study will help in the ongoing discussion on the role of phytoestrogens.