[Risks associated with phytoestrogen dietary supplementation and adjuvant hormonal therapy for breast cancer]

Adjuvant hormonal therapy using tamoxifen or aromatase inhibitors result in menopausal symptoms. Non-prescription dietary supplements containing plant-based phytoestrogens are often used to relieve menopausal symptoms. Phytoestrogens may reduce the action of tamoxifen and aromatase inhibitors. The purpose of this study is to gain insight into the potential risks of phytoestrogen supplementation during adjuvant hormonal therapy for breast cancer using tamoxifen or aromatase inhibitors.

Literature survey.

We performed a PubMed search for articles about studies on the effects of phytoestrogens on breast cancer treatment efficacy. We also searched on the basis of references in the articles we found in PubMed.

Studies based on in-vitro models as well as experimental animal models were identified. The studies on the interaction between phytoestrogen and tamoxifen showed contradictory results. The few studies pertaining to the interactive effect of phytoestrogens on aromatase inhibitors all showed a reduction in therapeutic efficacy of aromatase inhibitors caused by phytoestrogens.

The outcomes of the studies we found suggest that caution should be exercised when taking phytoestrogen in combination with either tamoxifen or aromatase inhibitors. We believe that patients with breast cancer should be informed of this as a matter of routine.