Diet High in Soy May Reduce Breast Cancer Recurrence in Postmenopausal Women
Soy is often discouraged as a dietary component for women with a history of breast cancer because the plant compound is a phytoestrogen that has a similar chemical structure to estrogen and can trigger estrogen-like actions in tissues, including the possibility of causing tumor growth. However, a new study has found that for some breast cancer survivors, soy isoflavones may actually reduce the risk of cancer recurrence.
Soy May Be Reduce Recurrence Risk in Hormone Sensitive Cancers
Researchers from the Cancer Hospital of Harbin Medical University in China began the study in 2002 which included 524 women between the ages of 29 and 72 who had been diagnosed with early or locally advanced breast cancer that was positive to estrogen receptors, progesterone receptors or both. Approximately half of all breast cancers that occur in premenopausal women and two-thirds among postmenopausal women are estrogen-sensitive.
The women participating in the study had had surgery and were receiving either tamoxifen or anastrozole, two drugs designed to stall tumor growth. The women completed a diet questionnaire at baseline that included questions about their consumption of soy products, such as tofu, soy milk, and soy flour. The researchers followed up on the women approximately 5 years later.
Post-menopausal breast cancer survivors who consumed the most soy isoflavones – just over 42 milligrams a day – had a 12.9 percent decreased risk of recurrence compared with those who consumed the least (about 15 mg). For women taking anastrozole, the effect was more pronounced at 18.7 percent lower.
The researchers note that they did not find the same association with premenopausal breast cancer survivors who had high soy consumption.
Women in the United States are not as likely to consume soy products on a daily basis as those in China. Only about 37% of Americans eat soy foods or drink soy beverages at least once a month or more, according to a 2010 study conducted by the United Soybean Board.
"Effect of soy isoflavones on breast cancer recurrence and death for patients receiving adjuvant endocrine therapy"
Xinmei Kang, Qingyuan Zhang, Shuhuai Wang, Xu Huang and Shi Jin, CMAJ 10.1503/cmaj.091298