Background: Some studies have investigated the association between soy and isoflavones consumption and breast cancer survival, but the results are far from conclusive. Accordingly, we performed a systematic review and meta-analysis to explore this issue.
Methods: We performed a comprehensive search of Web of Science, PubMed, and Embase from inception to January 2018. The summary hazard ratios (HRs) and 95% confidence intervals (CIs) were estimated using a random effects model.
Results: A total of 12 articles were included, which reported overall survival (OS), breast cancer specific survival (BCSS), and recurrence in 5770, 2386, and 1500 cases, respectively, among 37,275 women with breast cancer. The summary HR (95% CI) for the association (highest vs. lowest) of pre-diagnosis soy and isoflavones consumption with OS and BCSS was 0.84 (0.71-0.98) and 0.89 (0.74-1.07), respectively. Stratified analyses suggested that the reduced OS was more easily detected in studies that focused on post-menopausal patients. No significant association was found between post-diagnosis soy and isoflavones consumption with OS and BCSS, with summary HRs (95% CIs) of 0.80 (0.62-1.04) and 0.83 (0.64-1.07), respectively. Pre- and post-diagnosis soy isoflavones consumption were associated with reduced risk of recurrence.
Conclusion: This study provides limited evidence that pre-diagnosis soy and isoflavones intake is associated with a small reduction in post-menopausal breast cancer OS.
Keywords: Breast cancer; Breast cancer specific survival; Overall survival; Soy isoflavone.