soy effect varies by breast cancer subtype

[Lani]

in this study it seemed to be protective in ER+ and her2- (or those tumors which were both) breast cancer types only

Rather than protecting against breast cancer across the board, high soy food consumption appears to reduce the risk of estrogen receptor (ER)-positive and human epidermal growth factor receptor 2 (HER2)-negative tumors specifically, according to Japanese researchers reporting in the October 1 issue of the International Journal of Cancer.

Dr. Takeshi Suzuki, at Aichi Cancer Center Research Institute in Nagoya, and associates conducted a case-control study of 678 breast cancer cases 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 women with the highest soy intake who were ER-positive, HER2-negative or both.

For the top tertile of soy intake, compared to the lowest, the odds ratio (OR) was 0.74 for ER-positive breast cancer and 0.78 for HER2-negative breast cancer.

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

However, Dr. Suzuki's team found that "when the three receptors were jointly examined, a reduced risk was observed only in patients with ER-positive/PR-positive/HER2-negative tumor," with OR = 0.73 for those in the top tertile of soy consumption.

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

Int J Cancer 2008;123:1674-1680.