Asian women have lower breast cancer rates (39 per 100,000) than Western women (133 per 100,000) and, when Asian women migrate to the United States, their breast cancer rates tend to go up. This suggests that an environmental factor, perhaps related to diet, is at play.
Attention has zeroed in on soy products (consumed more in Asia) as they contain high quantities of isoflavones, molecules that affect pathways that could change breast cancer risk. Indeed, more and more women are taking high-dose soy or isoflavone supplements because of their perceived benefits, which include lowering LDL ("bad") cholesterol.
The questionnaire style of data collection makes some researchers leery. Nevertheless, the results are certainly interesting:
When the data was pooled, researchers found a 14 percent relative reduction in the risk of breast cancer among women who had a high soy intake. The association was somewhat higher in premenopausal women.
The scientists quoted didn't endorse soy supplements or refined soy products, but suggested foods like soy nuts and tofu may offer cancer protection.
You can read a lot about Dr. Fuhrman's thoughts on soy in these posts: