Dietary intake of phytoestrogens and phytoestrogen-rich foods in relation to survival after breast cancer in postmenopausal women

Background: Phytoestrogens – plant-derived estrogenic substances present in various foods – have been associated with postmenopausal breast cancer risk, but not much is known regarding its effect on survival. Methods: A follow-up study (MARIEplus) was conducted in 3,464 German postmenopausal breast cancer patients aged 50–74 years and diagnosed between 2001 and 2005 from a population-based case-control study. Vital status was ascertained via local population registries up to the end of 2009, and deaths were verified by death certificates. A top and bottom energy cutoff of 0.5% was used. Hazard ratios (HR) and 95% confidence intervals (CI) for baseline intake of six phytoestrogen-rich foods and four estimated dietary lignans in relation to overall mortality were assessed using Cox proportional hazards models, stratified by age at diagnosis and adjusted for study center and energy intake. Multivariate analyses were additionally adjusted for prognostic factors, such as stage, comorbidity, and ER/PR status. Results: Median follow-up time was 5.8 years, and 453 women deceased. Significantly decreased crude HRs were observed for high- versus non-consumers of all lignan-rich foods (HR=0.69, 95% CI=0.53–0.90) and of tofu (HR=0.51, 95% CI=0.29–0.92), respectively. After multivariate adjustment, only the effect of tofu remained significant. No associations were observed for other soy foods, rich in isoflavones. The lignans enterolactone and enterodiol were associated with a significantly lower overall mortality for higher compared to the lowest quantile of intake after adjustment (ptrend=0.016 and 0.002, respectively). The significantly decreased effects of lignan-rich foods and lignans were limited to ER-positive breast cancer. Results for breast cancer-specific mortality will also be presented. Conclusions: Postmenopausal breast cancer cases in Germany consuming high levels of lignans and lignan-rich foods may have an improved overall survival. This effect appears to be confined to ER-positive tumors.