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Soy Foods help Prevent Breast Cancer Recurrence - Studies

10/21/2010 22:47:00 admin

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Eating soy foods may help reduce risk of breast cancer recurrence in postmenopausal women who have undergone surgery for breast cancer, which is positive for estrogen and progesterone receptors, a new study suggests.

The study published on Oct 18, 2010 in Canadian Medical Association Journal also found an inverse association between soy consumption and risk of breast cancer recurrence in patients receiving anastrozole endocrine therapy.

For the study, Kang X. and colleagues examined the association between intake of soy isoflavones and risk of recurrence and death from breast cancer in 524 patients who underwent surgery for breast cancer from Aug 2002 through July 2003. Soy consumption was surveyed at baseline.

During a 5.1 year follow-up, no significant difference in the death rate was found between postmenopausal patients whose intake of soy isoflavones was in the highest quartile and those whose intake was in the lowest quartile.

However, postmenopausal women whose intake of soy isoflavones was in the highest quartile were 33 percent less likely to have breast cancer recurrence compared to those whose intake was in the lowest quartile.

Additionally, inverse associations were found in those who wee diagnosed with ER+/PR+ malignancy and those who receiving anastrozole as endocrine therapy.

The researchers concluded "High dietary intake of soy isoflavones was associated with lower risk of recurrence among postmenopausal patients with breast cancer positive for estrogen and progesterone receptor and those who were receiving anastrozole as endocrine therapy."

Other studies on soy isoflavones also pointed to a possibility that the soy phytochemicals may help prevent breast cancer recurrence.

One study published in the Nov 2009 issue of Breast Cancer Research and Treatment showed that among 1,954 female breast cancer survivors those who had highest intake of daidzein and glycetin were significantly less likely to have recurrence compared to no intake in postmenopausal women and among tamoxifen users. The subjects were followed for an average of 6.1 years after diagnosis.

Among tamoxifen users, those who had highest intake of daidzein, metabolite of soy protein, were 52 percent less likely to have breast cancer recurrence compared to those with lowest intake.

Guha N. at University of California at Berkeley and colleagues also found use of soy foods does not seem to interfere with tamoxifen efficacy.

Inconsistent with the current study, a study led by Shu X.O. and colleagues from Vanderbilt Epidemiology Center found highest intake of soy protein may help reduce risk of death from all causes by 29 percent and reduced recurrence risk by 32 percent compared to those who had lowest intake.

They also found an inverse association among women with either ER+ or ER- breast cancer and among both users and nonusers of tamoxifen.

Tamoxifen is a drug that is designed to interfere with the activity of estrogen, a female hormone that is known to promote cancer cell growths.

Tamoxifen can result in serious side effects including blood clots, strokes, uterine cancer and cataracts. Non-serious side effects include menopause-like symptoms like hot flashes, vaginal dryness, joint pain and leg cramps.

The drug is often given to breast cancer patients who have received treatment. The patients would be asked to take it for a number of years.

Soy isoflavones are known to be estrogenic. It is scientifically sound that soy estrogenic compounds may act like tamoxifen to interfere with the activity of estrogen and reduce the risk of recurrence of breast cancer.

Some doctors warned their patients of the soy phytoestrogens while many doctors prescribe bioidential or natural estrogen hormone, which is thousands or even tens of thousands times more potent than soy isoflavones, to women to help them overcome menopause symptoms.

But many studies have already linked estrogen therapy with increased risk of breast cancer and death from the disease.

One thing breast cancer patients should remember is that more than 80 percent of soy beans produced in the United States is genetically modified. The safety, according to some researchers, have not been rigidly tested. Some Russian studies have recently suggested that eating GM soy may cause damage.

More reports will be published here in the National Breast Cancer Awareness to help readers better understand the disease and how to prevent it.

By David Liu