Table 6.

Breast cancer: the pros and cons of polyphenols.

Pros

Cons

DNA protection by the anti-oxidant activity against carcinogens Decreased glucose uptake in cancer cells Cell cycle arrest, induction of pro-apoptotic and inhibition of anti-apoptotic proteins Modulation signaling pathways (reduced expression of plasma membrane receptors overexpressed in cancer, decreased phosphorylation of intracellular proteins) with implications in tumor growth, invasion and metastasis Generation of new classes of aromatase inhibitors based on the structure of polyphenols (flavones, isoflavones) Reduction in breast cancer risk in Chinese, Japanese women; reduction in breast cancer risk associated with high soy intake during adolescence Decreased risk of breast cancer recurrence (after daidzein intake)

So far not successful in preventing cancer in clinical trials Reduced bioavailability and stability Typically large concentrations have been used in most in vitro studies which are unlikely to be achieved in vivo The chemopreventive and therapeutic activity of polyphenols as single agents or in combination are studied in ongoing trials without final conclusions Heterogeneity in the applied doses, duration of administration, cells and animal models used in the studies