Effects of soy phytoestrogens genistein and daidzein on breast cancer growth.
OBJECTIVE
To determine whether genistein and daidzein, the major phytoestrogens in soy, can stimulate breast cancer growth.


RESULTS
Systematic search through primary English-language literature on MEDLINE (1966-January 2001), EMBASE (1982-January 2001) and Current Contents (1998-January 2001).


METHODS
Genistein and daidzein at low concentrations were found to stimulate breast tumor growth in in vitro and in vivo animal studies, and antagonize the antitumor effect of tamoxifen in vitro. At high concentrations, genistein inhibited tumor growth and enhanced the effect of tamoxifen in vitro.


CONCLUSIONS
Genistein and daidzein may stimulate existing breast tumor growth and antagonize the effects of tamoxifen. Women with current or past breast cancer should be aware of the risks of potential tumor growth when taking soy products.
de Lemos
M L
ML
Provincial Systemic Therapy Program, British Columbia Cancer Agency, Vancouver, Canada. mdelemos@bccancer.bc.ca
D000818:Animals; D016588:Anticarcinogenic Agents / Q000009:adverse effects* / Q000037:antagonists & inhibitors; D001943:Breast Neoplasms / Q000139:chemically induced*; D004305:Dose-Response Relationship, Drug; D004968:Estrogens, Non-Steroidal / Q000009:adverse effects*; D005260:Female; D019833:Genistein / Q000009:adverse effects*; D006801:Humans; D007529:Isoflavones / Q000009:adverse effects*; D048789:Phytoestrogens; D028321:Plant Preparations; D030262:Soybean Proteins; D013629:Tamoxifen / Q000037:antagonists & inhibitors*
D016588:Anticarcinogenic Agents; D004968:Estrogens, Non-Steroidal; D007529:Isoflavones; D048789:Phytoestrogens; D028321:Plant Preparations; D030262:Soybean Proteins; D013629:Tamoxifen; C004742:daidzein; D019833:Genistein