Soy isoflavones in cancer: molecular pathways, pharmacokinetic constraints and translational opportunities

Soy isoflavones are dietary phytoestrogens that have attracted considerable interest in cancer prevention and integrative oncology because of their ability to interact with estrogen receptor signaling and multiple cancer-related molecular networks. Researchers have investigated the major soy-derived isoflavones, particularly genistein, daidzein, and glycitein, across experimental, epidemiological, and clinical settings. Preclinical evidence indicates that these compounds can modulate key processes involved in tumor initiation and progression, including cell-cycle regulation, apoptosis, oxidative stress, inflammatory signaling, angiogenesis, epithelial–mesenchymal transition, and epigenetic regulation. These effects appear to involve coordinated regulation of ER, PI3K/Akt/mTOR, MAPK, Wnt/β-catenin, NF-κB, TGF-β, Nrf2, and non-coding RNA-associated networks, supporting their role as context-dependent biological modulators rather than conventional cytotoxic agents. Epidemiological studies generally report modest inverse associations between soy intake and selected malignancies, particularly breast and prostate cancers, although findings vary by tumor type, population, diet, and exposure assessment. Clinical translation remains constrained by discrepancies between in vitro exposure conditions and human pharmacokinetics, since circulating isoflavones occur mainly as glucuronide and sulfate conjugates with limited free aglycone exposure. Microbiota-dependent equol production further contributes to interindividual variability. This review synthesizes molecular, pharmacokinetic, metabolic, and translational evidence, positioning soy isoflavones as chemopreventive or adjunctive modulators requiring biomarker-guided clinical validation.