Gene mapping reveals soy's dynamic, differing roles in breast cancer

http://news.illinois.edu/news/15/0428Soy_WilliamHelferich.html

Sharita Forrest
April 28, 2015

Scientists have mapped the human genes triggered by the phytonutrients in soy, revealing the complex role the legume plays in both preventing and advancing breast cancer.

Researchers at the University of Illinois found that the compounds in minimally processed soy flour stimulate genes that suppress cancer, while purified soy isoflavones stimulate oncogenes that promote tumor growth. The paper, available online, was accepted for publication in the journal Molecular Nutrition and Food Research.

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Asian women’s risks for breast cancer tend to be three to five times lower than those of women in the U.S., which some researchers have attributed to Asian women’s consumption of soy-based whole foods, such as tofu and soy flour, across their lifespans.

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In the current study, the mice’s ovaries had been removed to simulate post-menopausal women, and Liu found that the soy flour and purified isoflavone diets had differing effects on their cells’ expression of genes associated with breast cancer.

The mice that consumed soy flour exhibited higher expression of the tumor-suppressing genes ATP2A3 and BLNK, each of which is associated with suppressed tumor growth. These mice also expressed lower levels of oncogenes MYB and MYC, which researchers have found to be critical to tumor growth during early stage breast cancer, and associated with the uncontrolled proliferation of cancer cells, respectively.

“Most important, we found that the soy flour strengthened the whole immune function, which probably explains why it does not stimulate tumor growth,” said Liu, who is completing both a doctorate in human nutrition and a master’s degree in statistics.

Conversely, the purified isoflavones stimulated tumor growth by activating oncogenes MYB and MYC, while suppressing both immune function and antigen processing, the body’s natural process of seeking out and destroying cancer cells.

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“There was a difference in the biological responses of mice that consumed the soy flour and those that consumed isoflavone supplements, although both diets contained the same amount of the phytoestrogen genistein,” Liu said. “The findings suggest that it’s advisable for women with breast cancer to get isoflavones from soy whole foods, rather than isoflavone supplements.”

Helferich, a co-author on the paper, said purified isoflavones behave similarly to estrogens such as estradiol, which prior studies have linked with the growth and proliferation of breast cancer cells.

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In another new study at Illinois, researchers found that soy isoflavones enhanced the growth of bone micro-tumors in mice with estrogen-responsive breast cancer, causing the tumors to metastasize more aggressively from bone to lung. Xujuan Yang, an associate researcher in Helferich’s laboratory, led that project.

The mice that consumed an isoflavones diet had triple the number of tumors – and had larger tumors – on their lungs, compared with their counterparts in the control groups, Yang found. A paper on the study was published in the April issue of Clinical and Experimental Metastasis.

“The main take-home message is, if you have breast cancer, isoflavone dietary supplements are not recommended,” Helferich said. “However, consuming soy from a whole food – along with other legumes – is likely safe.”