Effects of soy isoflavone and endogenous oestrogen on breast cancer in MMTV-erbB2 transgenic mice

Abstract

OBJECTIVE: Soy isoflavone is associated with modification of breast cancer risk. Effects of dietary isoflavone on breast tissue carcinogenesis under varying endogenous oestrogen contexts were investigated. METHODS: Five-week-old mouse mammary tumour virus (MMTV)- erbB2 female transgenic mice (n = 180) were divided into three equal groups: low-, normal- and high-oestrogen groups. Each group was then subdivided into an experimental group (given soybean feed) and a control group (given control feed). RESULTS: In the high-oestrogen environment, breast cancer incidence was significantly lower in the experimental versus the control group, whereas in the low-oestrogen environment, breast cancer incidence was significantly higher in the experimental versus the control group. There were no between-group differences in mean breast tumour latency, mean largest tumour diameter and breast tumour tissue vascular endothelial growth factor levels. CONCLUSIONS: Dietary soy isoflavones promote breast cancer at low oestrogen levels but inhibit breast cancer at high oestrogen levels. This effect may only occur during the initiation stage of breast cancer. © SAGE Publications Ltd 2012.