Dietary phytoestrogens and biomarkers of their intake in relation to cancer survival and recurrence: a comprehensive systematic review with meta-analysis

Context: Recent studies have outlined the potential role of dietary factors in patients who have survived cancer. Objective: The aim of this study was to summarize the evidence of the relation between dietary intake of phytoestrogens and their blood biomarkers and, overall, cancer-specific mortality and recurrence in patients with cancer. Data Sources: A systematic search of PubMed, EMBASE, and Web of Science databases of studies published up to September 2019 was performed. Databases were searched for prospective and retrospective cohort studies reporting on dietary phytoestrogen intake and/or blood biomarkers and the outcomes investigated. Data extraction: Data were extracted from each identified study using a standardized form. Data analysis: Twenty-eight articles on breast, lung, prostate, and colorectal cancer, and glioma were included for systematic review. Given the availability of studies, a quantitative meta-analysis was performed solely for breast cancer outcomes. A significant inverse association among higher dietary isoflavone intake, higher serum/plasma enterolactone concentrations, and overall mortality and cancer recurrence was found. Among other cancer types, 2 studies reported that higher serum enterolactone and higher intake of lignans were associated with cancer-specific survival for colorectal cancer and glioma, respectively. Conclusions: Dietary phytoestrogens may play a role in survival from breast cancer; evidence regarding other cancers is too limited to draw any conclusions.