Positive Health Online

Abstract

ALLRED and colleagues, Department of Food Science and Human Nutrition, University of Illinois, Urbana, Illinois 61801, USA, investigated whether soy isolates of the isoflavone genistein would stimulate the growth of oestrogen-dependent breast cancer cells in mice in a dose-dependent manner.

Background

This research group previously showed that the isoflavone genistein stimulated the growth of oestrogen-dependent human breast cancer cells (MCF-7) in vivo (Hsieh CY et al. Cancer Research 58: 3833-38, 1998). Isoflavones are phytoestrogens present in high concentrations in soy. Whether consumption of soy-protein-derived genistein stimulates oestrogen-dependent tumour cells in a manner similar to pure genistein has not been investigated in the athymic mouse tumour implant model.

Methodology

Soy protein isolates were fed to athymic mice implanted subcutaneously with oestrogen-dependent tumours. Genistein contents of the soy isolate diets (aglycone equivalent) were 15, 150 and 300 ppm. Positive (with 17beta-oestradiol pellet implant) and negative (no 17beta-oestradiol) control groups were fed casein-based (isoflavone-free) diets. Tumour size was measured weekly. At the end of the study, the tumours were collected for evaluation of cell proliferation (by measuring incorporation of bromodeoxyuridine into cellular DNA) and oestrogen-dependent gene expression (pS2 mRNA being used as an oestrogen-responsive gene).

Results

Soy protein diets containing varying amounts of genistein increased oestrogen-dependent tumour growth in a dose-dependent manner . Cell proliferation was greatest in tumours of mice given oestrogen or dietary genistein (150 and 300 ppm).

Conclusion

The results provide new information that soy protein isolates containing increasing concentrations of the isoflavone genistein stimulate dose-dependently the growth of oestrogen-dependent breast cancer cells in vivo.

References

Allred CD et al. Soy diets containing varying amounts of genistein stimulate growth of estrogen-dependent (MCF-7) tumors in a dose-dependent manner. Cancer Research 61 (13): 5045-50. Jul 2001.

Comment

The results of this research study will add yet more fuel to the growing scientific controversy regarding the safety or otherwise of soy. A fairly comprehensive overview of this research is provided on our internet website.