Soy reduces breast cancer risk by receptor status

Rather than protecting against all breast cancers, high levels of soy food consumption appears to specifically reduce the risk of estrogen receptor (ER)-positive tumors and human epidermal growth factor receptor 2 (HER2)-negative tumors, Japanese researchers report in the International Journal of Cancer.

Dr. Takeshi Suzuki, at Aichi Cancer Center Research Institute in Nagoya, and associates conducted a study of 678 women with breast cancer and 3,390 controls matched by age and menopausal status with no history of cancer.

The researchers "observed a significantly reduced risk" of breast cancer among the women who ate the most soy and were ER-positive, HER2-negative or both.

For women who ate the most soy compared with those who ate the least amount the odds of having ER-positive breast cancer were reduced by 26 percent and for women with HER2-negative breast cancer, the reduced risk was 22 percent.

Soy intake was not significantly associated with HER2-positive or ER-negative tumors, or with the presence or absence of the progesterone receptor (PR).

However, Suzuki's team found that "when the three receptors were jointly examined, a reduced risk was observed only for patients with ER-positive/PR-positive/HER2-negative tumors," with a 27-percent reduction seen only in the women who ate the most soy.

"These findings are biologically plausible, and suggest a potential benefit of soybean products in the prevention of breast cancer," the investigators conclude.

SOURCE: International Journal of Cancer, October 2008.