The dietary supplement genistein can undermine breast cancer...( CHAMPAIGN Ill. Women taking aromata...)

CHAMPAIGN, Ill. Women taking aromatase inhibitors to treat breast cancer or prevent its recurrence should think twice before also taking a soy-based dietary supplement, researchers report.

Genistein, a soy isoflavone that mimics the effects of estrogen in the body, can negate the effectiveness of aromatase inhibitors, which are designed to reduce the levels of estrogens that can promote tumor growth in some types of breast cancer.

The new study, which included researchers from the University of Illinois, Virginia Polytechnic and State University and the National Center for Toxicological Research, appears in the journal Carcinogenesis.

Aromatase inhibitors are a mainstay of breast cancer treatment in post-menopausal women. These drugs work by interfering with the enzyme aromatase, which catalyzes a crucial step in converting precursor molecules to estradiol, the main estrogen in the body.

About two-thirds of all cases of breast cancer diagnosed in the U.S. are estrogen dependent or estrogen sensitive, which means that the tumors grow more rapidly in the presence of estrogen.

Most women diagnosed with breast cancer are post-menopausal, so their ovaries are no longer producing normal levels of estrogen. Other tissues, however, produce a steroid hormone, androstenedione (AD), which with the help of aromatases is converted to testosterone and estrogens. The estrogens produced from AD can stimulate the growth of some types of breast cancer tumors.

The researchers conducted several trials in a mouse model of estrogen-dependent post-menopausal breast cancer. First, they gave the mice AD, which was converted to estrogen and created a high estrogen environment.

This helped the researchers determine the maximum growth rate of the breast cancer tumors.

Next, they added Letrozole, an aromatase inhibitor widely prescribed to post-menopausal women with estrogen-dependent breast cancer. Th
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