This is a really interesting and important discussion. I have a few comments about phytoestrogens which I suspect will also be relevant to phyto-androgenic herbs too.


First of all there is an assumption that phytoestrogens are to be avoided by women with breast cancer. The logic here is obvious but way too over simplistic and at odds with the evidence. At the moment there is some reasonable data to support the use of phytoestrogenic herbs in women with oestrogen receptive breast cancer. The physiology is complex and appears to be quite rapidly evolving. As is often the case when you scratch the surface simple assumptions are over-simplistic when it comes to what really happens in a living body (this is clearly demonstrated in drugs like tamoxifen which has an antagonistic effect to oestrogen in breast tissue but an agonistic (pro) oestrogenic effect on endometrial and bone tissue).


I can supply a few interesting papers and abstracts for anyone who wants to have a more detailed exploration of the subject. I should stress again that the data is complex, contradictory, almost certainly incomplete. You will not get a definitive and simple answer to the question of whether phytoestrogens are safe to use in women with breast cancer but, to my mind, I think there is enough positive epidemiological data and experimental data to support the continued use of herbal medicines for this population. Some of the main points are:


  1. Epidemiological evidence suggests that phytoestrogens have a protective effect on breast cancer-especially if taken in reasonably large quantities and by pre-pubescent girls. Countries such as Japan where women consume high levels of phytoestrogens from soya have approx. 1/3rd the rates of breast cancer as are found in developed western countries.


A relatively recent study (JAMA. 2009;302:2437-2443, 2483-2484) in Shanghai on over 5000 women diagnosed with breast cancer found that higher levels of soy consumption (up to 11g/day) were associated with reduced rates of recurrence and mortality.


  1. There are at least 2 types of oestrogen receptor (ER) ER-a and ER-b. ER-a activation triggers cell proliferation whilst ER-b appears to have a moderating effect on this proliferation and activates other, non proliferative ER pathways that, for example may reduce menopausal-like symptoms such as hot flashes. Phytoestrogens tend to activate ER-b receptors.


  1. The attached paper on in vitro Si Wu Tang shows that the formula does have an oestrogenic effect but does not appear to activate some known oncogenes that have been associated with breast cancer. The paper also suggests that any proliferative effect on breast cancer cells is mitigated by the concurrent use of tamoxifen.


  1. Phytoestrogens may inhibit the action of aromatase-the enzyme that converts androgens to oestrogen’s. Aromatase inhibitors are a mainstay treatment to help prevent breast cancer recurrence in post-menopausal women.


  1. Dosage is important as vitro research on breast cancer cell lines suggests that low dosages of common phytoestrogens eg genistein can stimulate cancer cell line proliferation but higher dosages inhibit it. (The question for herbalists is then what constitutes a high and a low dose. I can’t give you the answer to that and the data is once again contradictory on dietary phytoestrogens but the Shanghai study of 11g of soya suggests that a reasonably robust CHM formula will constitute a higher dose-sorry can’t be more precise than that!)


  1. Phytoestrogens have an affinity to bind to oestrogen receptors of between 1,000 to 10,000 times less than endogenous oestradiol…not the same as 1,000 times less of a physiological effect but it does suggests reduced physiological impact.



The argument is far from straight forward but, as I said, I do believe there is sufficient supportive evidence to warrant the use of herbal medicines for women (and men) with hormone sensitive cancers.