Phytoestrogens and breast cancer –promoters or protectors?

Abstract

The majority of breast cancers are oestrogen dependent and in postmenopausal women the supply of oestrogens in breast tissue is derived from the peripheral conversion of circulating androgens. There is, however, a paradox concerning the epidemiology of breast cancer and the dietary intake of phytoestrogens that bind weakly to oestrogen receptors and initiate oestrogendependent transcription. In Eastern countries, such as Japan, the incidence of breast cancer is approximately one-third that of Western countries whilst their high dietary intake of phytoestrogens, mainly in the form of soy products, can produce circulating levels of phytoestrogens that are known experimentally to have oestrogenic effects. Indeed, their weak oestrogenicity has been used to advantage by herbalist medicine to promote soy products as a natural alternative to conventional hormone replacement therapy (HRT). Such usage could increase in light of recent evidence that long-term HRT usage may be associated with an increased risk of breast cancer with a consequent reduction in prescription rates. So, are phytoestrogens safe as a natural alternative to HRT and could they be promoters or protectors of breast cancer? If they are promoters, then we must assume that it is due to their oestrogenic effect. If they are protectors, then other actions of phytoestrogens, including their ability to inhibit enzymes that are responsible for converting androgens and weak oestrogens into oestradiol, must be considered. This paper addresses these questions by reviewing the actions of phytoestrogens on oestrogen receptors and key enzymes that convert androgens to oestrogens in relation to the growth of breast cancer cells. In addition, it compares the experimental and epidemiological evidence pertinent to the potential beneficial or harmful effects of phytoestrogens in relation to the incidence/progression of breast cancer and their efficacy as natural alternatives to conventional HRT.

Combating Malaria with Plant Molecules: A Brief Update

“…This has been linked to differences in the diet with a different intake of phytoestrogens, mainly in the form of soy products [18, 19]. Similarly, a lower incidence of prostate cancer in Asia has been correlated with high consumption of soy isoflavones [20].…”

Breast Cancer, Estrogen Receptor and Ligands

“…Phytoestrogens are plant-derived chemicals that have estrogenic activity, combining with ERs and initiating estrogen-dependent transcription [134,135]. They are classified as several different groups according to their chemical structure: isoflavones, flavones, flavanones, coumestans, stilbenes, and lignans.…”

“…They are classified as several different groups according to their chemical structure: isoflavones, flavones, flavanones, coumestans, stilbenes, and lignans. The most widely studied are the isoflavones, present in high concentrations in soy products and red clover [136], followed by the flavones and then coumestans [134]. The active compounds investigated usually as ER ligands and for chemopreventing and treating breast cancer have a linear chemical structure similar to that of E2 (Fig.…”

“…The active compounds investigated usually as ER ligands and for chemopreventing and treating breast cancer have a linear chemical structure similar to that of E2 (Fig. 22) [134,137,138], so that they can bind to ERa with the Type-I mode and to ERb.…”

“…For the investigation of phytoestrogens, the key questions are whether or not and how they act as anticancer drugs or chemopreventing agents; should they be consumed (or not) at very high levels in the diet, or should they rather (or not) be taken as medicine, because they are already more or less present in the daily food. There is still no conclusive evidence that a high dietary intake of phytoestrogens and the reduced incidence of breast cancer are directly related [134]. But as ER ligands, varieties of phytoestrogens remain in binding to the ER and breast cancer.…”