Soy Isoflavones and Breast Cancer Recurrence: A Systematic Review and Meta-Analysis of Observational Studies

Abstract

Introduction: The safety of soy consumption in breast cancer survivors is controversial due to the phytoestrogenic activity of isoflavones. This review aims to clarify the association between soy isoflavone intake and breast cancer recurrence.

Methods: A search of MEDLINE and Embase was performed for prospective observational studies that assessed soy intake after a breast cancer diagnosis and reported on recurrence or mortality. Hazard ratios (HR) were pooled using a random-effects model.

Results: The meta-analysis included 11 studies with over 35,000 participants. Higher soy isoflavone intake was associated with a significant reduction in the risk of breast cancer recurrence (Pooled HR = 0.85, 95% CI: 0.77-0.93). The protective association was observed for both ER-positive and ER-negative tumors and was not diminished in patients taking tamoxifen.

Discussion: Contrary to earlier concerns, this systematic review finds that soy consumption after a breast cancer diagnosis is associated with a lower risk of recurrence. This suggests that the phytoestrogenic activity of isoflavones may be beneficial.

Conclusion: Soy intake appears safe and is associated with a reduced risk of recurrence in breast cancer survivors.