Isoflavones and cancer

Anti-estrogenic activity

Hormone-related cancers, such as breast cancer and prostate cancer, are much rarer in countries where the food is rich in soy isoflavones

Estrogen is needed for the development of the breasts and other female characteristics. But estrogens can also be dangerous, because the encourage the growth of tumors in the breast. Isoflavones, especially genistein, lower the effect of the estrogens by binding with the estrogen receptors. Isoflavones don't have the negative effect on cell division. Isoflavones will act as anti-estrogen in a similar way as Tomoxifen, a drug widely used for the treatment and prevention of breast cancer.

Isoflavones also promote the binding of the hormones estrogen and testosterone to SHBG (Sex Hormone Binding Globulin) proteins, which are responsible for the transport of sex hormones in the body. Isoflavones stimulate the production of SHBG, thereby reducing the concentration of the free hormones, which means that the proneness to cancer is reduced.

Anti-tumor effects not related to estrogen activity

Isoflavones inactivate an array of enzymes involved in the cancer process such as tyrosine kinase and aromatase-5a-reductase. Enhanced activity of tyrosine kinases has been implicated with many cancers. In vitro tests have shown that genistein can inhibit the activity of tyrosine kinase. Genistein inhibits particularly the nutrition of the tumor, by reducing the formation of the blood vessels in the tumor, thereby slowing down the tumor’s growth. Angiogenesis is a process of the formation of new blood vessels to feed the tumor. Genistein is the most potent plant derived angiogenesis inhibitor.

The isoflavones also act as an antioxidant. Similar to vitamin C and E, isolfavones neutralize the free radicals which play an important role in the mutagenesis and carcinogenesis.

More literature about isoflavones and tumor

Prevention of spontaneous prostate-related cancer in Lobund-Wistar rats by a soy protein isolate - isoflavone diet. Prostate 2000 Oct 1;45(2):101-5

Soy isoflavones in the treatment of prostate cancer. Nutr Cancer 2003;47(2):111-7

Soy, isoflavones, and breast cancer risk in Japan. Journal of the National Cancer Institute, Vol. 95, No. 12, 906-913, June 18, 2003

Dietary Soy Isoflavones and Estrone Protect Ovariectomized ERKO and Wild-Type Mice from Carcinogen-Induced Colon Cancer. Journal of Nutrition:179-182, January 2004

Chemoprevention of Breast Cancer, Proteomic Discovery of Genistein Action in the Rat Mammary Gland. Journal of Nutrition, 135:2953S-2959S, December 2005