“Based on our results, we do not see a detrimental effect of soy food intake among women who were treated with endocrine therapy,” said Dr. Zhang. “For women with hormone receptor-negative breast cancer, soy food products may potentially have a protective effect. Women who did not receive endocrine therapy as a treatment for their breast cancer had a weaker, but still statistically significant, association.”
More than 20 percent of all new breast cancer cases with known estrogen and progesterone receptor status are receptor-negative, and they have poorer survival rates than hormone receptor-positive cases. “Whether lifestyle factors can improve survival after diagnosis is an important question for women diagnosed with this more aggressive type of breast cancer. Our findings suggest that survival may be better in patients with a higher consumption of isoflavones,” said senior author Esther John, PhD, of the Cancer Prevention Institute of California. The investigators noted that they examined only naturally occurring dietary isoflavones, not isoflavones from supplements.
How isoflavones from foods interact with breast cancer cells is unclear, but research has shown that they have antioxidant, anti-inflammatory, anti-angiogenic, and other effects that could influence tumor survival and growth.
In an accompanying editorial, Omer Kucuk, MD, of the Winship Cancer Institute of Emory University, noted that the United States is the number 1 soy producer in the world and is in a great position to initiate changes in health policy encouraging soy intake. “We now have evidence that soy foods not only prevent breast cancer but also benefit women who have breast cancer. Therefore, we can recommend women to consume soy foods because of soy’s many health benefits,” he wrote.