The largest study examining the relationship between the traditional soy-rich Japanese diet and development of prostate cancer in Japanese men has come to a seemingly contradictory conclusion: intake of isoflavone chemicals, derived largely from soy foods, decreased the risk of localized prostate cancer but increased the risk of advanced prostate cancer.
The prospective study of 43,509 men, published in the March issue of Cancer Epidemiology, Biomarkers & Prevention, suggests that the effects of isoflavones on prostate cancer development may differ according to disease stage, say researchers at the National Cancer Center in Japan.
One possible explanation is that isoflavones may delay the progression of latent prostate cancer only; once tumors lose estrogen-receptor beta expression and become aggressive, isoflavones may fail to protect against the development of advanced cancer, and might even increase the risk of progression, possibly by reducing serum testosterone, researchers say. It is also possible that advanced and localized prostate cancer may be different tumor subtypes, which may react differently to isoflavones.
http://www.eurekalert.org/pub_releases/2007-03/aafc-sfp031507.php
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