Consumption of Soy and Cancer

Soy may promote overexpression of breast cancer genes in some women.

Soy and products made from it, like soy milk and tofu, could have an effect on genes involved in breast cancer growth. Researchers at Memorial Sloan Kettering have recently uncovered evidence that addresses soy.

In a controlled, randomized study of women with newly diagnosed, early-stage breast cancer, MSK scientists found that, in a subset of participants, adding a moderate amount of soy to the diet led to an increase in the expression of genes associated with cancer growth.

In a small portion of the women in the study, there was evidence that genes that promote proliferation were overexpressed.

The study was not long enough to address the question of whether these changes in gene expression would lead to enhanced tumor growth. Although the genes were being expressed, it is not clear that this will translate into actual tumor growth, but the concern is that there may be the potential.

The findings were published in the September 4 issue of the Journal of the National Cancer Institute.

Study participants had recently undergone breast biopsies and were diagnosed with stage 1 or 2 breast cancer and scheduled to have a mastectomy or lumpectomy two to three weeks later. During the time between their diagnosis and surgery, the women were randomized to receive either soy protein or a placebo as part of the study.

From the original pool of participants, those in the soy group who had high levels of genistein, a component of soy, were evaluated along with patients in the control group who did not take soy to look for signs of changes in gene expression or molecular changes in their tumors.

Not everyone who took the soy had high levels of genistein - and changes in gene expression were seen only in patients who did experience an increase. 20 percent of those patients who took the soy had really high levels of the genistein metabolite.

Of the women with high genistein levels, a few of them experienced changes in a specified set of genes that are established to be involved in breast cancer cell growth, death, or some aspect of breast cancer pathology.