SAN ANTONIO — A compound in soy believed to protect against breast cancer revs up production of a protein that suppresses cancer in healthy breast cells, a new lab-dish study shows. The finding provides biological data in support of survey research suggesting that a diet high in soy is the reason why women in Asian nations face a lower risk of breast cancer than do Western women.

Soy isoflavone genistein boosts levels of the well-known tumor-suppressor protein PTEN, say molecular biologist Omar Rahal and endocrinologist Rosalia Simmen of the University of Arkansas for Medical Sciences in Little Rock. They presented these preliminary findings December 13 in Texas at the San Antonio Breast Cancer Symposium.

Previous lab investigations of soy’s effect on PTEN production in breast tissues have looked at the effects of high doses of isoflavone genistein on cancer cells. In this study, the researchers used amounts of the soy compound that replicate the levels in the blood stream of people who regularly consume soy products. And, the team tested the compound in a cell line of healthy tissue with characteristics of pre-pubescent breast cells.

“We were looking for early epigenetic changes that can have an impact later in life,” says Rahal. What the team found was increased activity of the gene that encodes the PTEN protein.

The lab-dish study showed that cells exposed to soy isoflavone genistein gin up production of PTEN protein in the nucleus, as well as p53, another tumor-suppressor protein. This resulted in less cell proliferation, the scientists report.

The findings support a hypothesis that a diet rich in soy "can modify this mammary gland and make it more resistant to future carcinogenic insults," says Rahal.

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