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What every woman must know about soy and breast cancer

Kathleen Blanchard's picture
Timing of soy consumption linked to breast cancer risk, recurrence

Researchers have found more about soy and breast cancer making it important for women to know when eating soy could be beneficial and when it could harm.


Georgetown Lombardi Comprehensive Cancer Center researchers have uncovered some new information based on animal testing that could clear up some questions about the link between soy and breast cancer.

Does soy prevent or promote breast cancer?

Based on the new findings it seems soy may not pose an extra risk for breast cancer development or recurrence, but with caveats.

Based on biological soy pathways studied in mouse models the researchers discovered it's all about timing of soy consumption.

The study, published in Clinical Cancer Research, suggests genistein - an isoflavon in soy - can affect tamoxifen in two different ways, which also correlates what has been seen in breast cancer patients.

"There has long been a paradox concerning genistein, which has the similar structure as estrogen and activates both human estrogen receptors to a degree," Leena Hilakivi-Clarke, PhD, professor of oncology at Georgetown Lombardi said in a media release.

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Hilavi-Clarke also points out soy intake among Asian women has been associated with a five-fold lower rate of breast cancer, compared to Western women.

The reason breast cancer rates are so much lower in Asia where soy consumption is high has been a mystery, prompting ongoing research.

Xiyuan Zhang, PhD., lead study investigator says sustained exposure to genistein in soy provided protection against breast cancer development and reccurence.

Researchers also found soy can boost the effect of the Tamoxifen by inhibiting a mechanism that helps cancer cells survive.

See: Plant compound may reduce risk of breast cancer

Soy harmful with breast cancer diagnosis

Soy can be harmful if introduced into the diet after breast cancer develops the researchers found. Genistein made breast cancer tumors in rats more resistant to Tamoxifen. Zhang said they don't know why it happens.

Hilakivi-Clarke advises: "Our results suggest that breast cancer patients should continue consuming soy foods after diagnosis, but not to start them if they have not consumed genistein previously,"