Women with the highest average intakes of more than 23 mg per day of soy isoflavones had a 9 percent reduced risk of mortality and a 15 percent reduced risk for recurrence, compared to women with the lowest average intakes, but the results were not statistically significant, reported Xiao Ou Shu, MD, PhD, from Vanderbilt University Medical Center.
"Soy foods contain large amounts of isoflavones that are known to bind to estrogen receptors and have both estrogen-like and anti-estrogenic effects,” explained Dr Shu. “There are concerns that isoflavones may increase the risk of cancer recurrence among breast cancer patients because they have low estrogen levels due to cancer treatment.
“We're particularly concerned that isoflavones may compromise the effect of tamoxifen on breast cancer treatment because both tamoxifen and isoflavones bind to estrogen receptors."
Soy isoflavones intakes for 16,048 of these women breast cancer survivors indicated however, that such concerns are not observed in the populations studied, according to data presented at the American Association for Cancer Research’s (AACR) 102nd Annual Meeting 2011.
"Our results indicate it may be beneficial for women to include soy food as part of a healthy diet, even if they have had breast cancer," said Dr Shu. "This can't be directly generalized to soy supplements, however, as supplements may differ from soy foods in both the type and amount of isoflavones."