dietary supplement genistein can undermine breast cancer treatment

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Public release date: 23-Sep-2008

http://www.eurekalert.org/pub_releases/2008-09/uoia-tds092308.php

Contact: Yates

diya@...

University of Illinois at Urbana-Champaign

The dietary supplement genistein can undermine breast cancer treatment

Many supplements sold without a prescription and marketed to

post-menopausal women include plant compounds, such as genistein, that

can block the effectiveness of Letrozole, a breast cancer drug.

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. This

treatment (Letrozole) effectively blocked the effects of AD and the

breast cancer tumors stopped growing.

But when they added genistein (a plant estrogen or " phytoestrogen "

present in many dietary supplements) to the mix, the researchers

observed a dose-dependent reduction in the effectiveness of the breast

cancer drug. Specifically, the tumors began to grow again. They grew

fastest at the highest dietary doses of genistein.

" To think that a dietary supplement could actually reverse the effects

of a very effective drug is contrary to much of the perceived benefits

of soy isoflavones, and unsettling, " said Helferich a professor

of food science and human nutrition at Illinois and principal

investigator on the study. " You have women who are taking these

supplements to ameliorate post-menopausal symptoms and assuming that

they are as safe as consuming a calcium pill or a B vitamin. "

Many women take genistein supplements to control hot flashes and other

symptoms of menopause. The researchers found that the doses commonly

available in dietary supplements were potent enough to negate the

effectiveness of aromatase inhibitors.

" These compounds have complex biological activities that are not fully

understood, " Helferich said. " Dietary supplements containing soy-based

phytoestrogens provide high enough dosages that it could be a

significant issue to breast cancer patients and survivors. "

Plant estrogens from soy are not the only ones of concern, Helferich

said. In a recent study, he and his colleagues found that certain

mixtures of estrogenic botanical components and extracts marketed as

supplements to assist " female libido enhancement " and sold without a

prescription appeared to spur breast cancer tumor growth at low doses,

while having no effect on tumors at high doses.

That study appeared last year in Food and Chemical Toxicology.

" We are just starting to understand the complex effects of the dietary

supplements that contain phytoestrogens, " Helferich said. " There is an

ongoing human experiment in which the outcome is unknown. These findings

raise serious concerns about the potential interaction of the estrogenic

dietary supplements with current breast cancer therapies. "

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Editor's note: To reach Helferich, call ; e-mail:

helferic@...

--

ne Holden, MS, RD

" Ask the Parkinson Dietitian " http://www.parkinson.org/

" Eat well, stay well with Parkinson's disease "

" Parkinson's disease: Guidelines for Medical Nutrition Therapy "

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