The soy and breast cancer controversy has been around a long time. It persists despite an abundance of human research supporting the safety and possible benefit of soyfood consumption by breast cancer patients. In general, health professionals are aware of this research. Hopefully, this information will be efficiently conveyed to the public at large.
It’s been about 20 years since the controversy began in earnest. Conceptually, the estrogen-like effects of isoflavones, which were recognized in the 1950s, provided a theoretical basis for concern.1 However, the prevailing view among scientists through the first half of the 1990s, was that soyfoods would function as anti-estrogens and reduce the risk of breast cancer, perhaps improving the prognosis of breast cancer patients. In the 1990s, the estrogen receptor antagonist, tamoxifen, was the drug of choice for treating patients with estrogen-sensitive breast cancer.2
The view of soyfoods and isoflavones began to change quite dramatically beginning in the late 1990s because of findings from a series of mouse studies that began to be published.3 These studies showed that the isoflavone genistein stimulated the growth of existing estrogen-sensitive tumors in athymic ovariectomized mice implanted with human estrogen receptor-positive human breast cancer cells. Despite subsequently published clinical and epidemiological studies refuting these studies, the soy-breast cancer controversy is still with us today.