Soy shows potential for men
with prostate cancer

Part of the pea family, soy is a plant that is commonly found in southeastern Asia. It makes up a large part of the Asian diet (in foods like tofu and tempeh). Because the rate of prostate cancer is very low in Asia, its high consumption is believed to play a role in cancer prevention.

Soy products and some of its components—which are called isoflavones—have been widely studied for their effects on cancer, including prostate cancer. Researchers believe that some isoflavones (in particular one called genistein) may have estrogen-like effects. What isn’t yet clear is whether isoflavones have the ability to stimulate or stop the effects of the hormone estrogen.

Here are results of some recent studies which point to the potential benefits in men with prostate cancer:

• Perabo et all reviewed all experimental preclinical laboratory studies and animal studies data, as well as clinical trials assessing the isoflavone genistein for the prevention and treatment of advanced prostate cancer. The preclinical data and animal studies showed activity against cancer cells, but more studies are needed to determine if genistein would have the same cancer-killing effect in humans
• Payton-Stewart et al found in a laboratory study that glyceollins, which are soy-derived phytoalexins, inhibited growth in human prostate cancer cells that was similar to the effect from genistein
• Pendleton et al concluded from a Phase II study of 20 men with a rising PSA after prior local therapy that dietary intervention with isoflavone supplements may have biologic activity in men with biochemical recurrent prostate cancer. In this study, men drank soy milk containing 47 mg of isoflavonoid per 8 oz serving 3 times per day for a year. PSA had increased 56% per year before the men entered the study, and only increased 20% per year for the 12-month study period. While this was a small study, the decline in the slope of PSA results was statistically significant
• Yan and Spitznagel did an extensive review of all the available data (called a meta analysis) and concluded that dietary soy is associated with a reduced risk of prostate cancer. They also concluded that this benefit may be due to the type of products a man consumes and how much he consumes

Hopefully, researchers, nutritionists, and prostate cancer specialists will work together to provide guidelines for what types of foods and/or supplements are ideal for men with prostate cancer, and how much men should consume each day. Studies should also be conducted to determine if long-term consumption is safe for men with cancer.

When we last checked the National Institutes of Health clinical trial database, there were 14 clinical trials (some completed and some underway) that are being conducted in this area in men who have prostate cancer. Previously, most of the research studies have been laboratory studies.

Updated 4/09



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References:

Payton-Stewart F, Schoene NW, Kim YS, Burow ME, Cleveland TE, Boue SM, Wang TT. Molecular effects of phytoalexin glyceollins in human prostate cancer cells LNCaP. Mol Carcinog. 2009. Mar 4. [Epub ahead of print.]

Pendleton JM, Tan WW, Anai S, Chang M, Hou W, Shiverick KT, Rosser CJ. Phase II trial of isoflavone in prostate-specific antigen recurrent prostate cancer after previous local therapy. BMC Cancer. 2008;5(8):132.

Perabo FG, Von Löw EC, Ellinger J, von Rücker A, Müller SC, Bastian PJ. Prostate Cancer Prostatic Dis. 2008;11(1):6-12.

Yan L, Spitznagel EL. Soy consumption and prostate cancer risk in men: a revisit of a meta-analysis. Am J Clin Nutr. 2009;89(4):1155-63.