A new study has revealed that soy food consumption does not increase the risk of cancer recurrence or death among survivors of breast cancer.
Researchers investigated the association between soy food intake and breast cancer outcomes among survivors, using data from a multi-institution collaborative study, the After Breast Cancer Pooling Project.
"There has been widespread concern about the safety of soy food for women with breast cancer," said lead researcher Xiao Ou Shu, professor of medicine at Vanderbilt Epidemiology Center, 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."
"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," he said.
Together study included 18,312 women between the ages of 20 and 83 years who had invasive primary breast cancer.
Soy isoflavones intake was assessed for 16,048 of these women on average of 13 months after breast cancer diagnosis using food frequency questionnaires for a group of soy isoflavones in three cohorts and on tofu and soy milk consumption in one cohort.
Breast cancer outcomes were assessed, on average, nine years after cancer diagnosis.
Outcomes among the survivors who consumed the highest amounts of soy isoflavones (more than 23 mg per day) were compared with the outcomes of those whose intake was lowest (0.48 mg per day or lower).
Women in the highest intake category of more than 23 mg per day had a 9 per cent reduced risk of mortality and a 15 per cent reduced risk for recurrence, compared to those who had the lowest intake level.
"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 Shu.
The study was presented at the AACR 102nd Annual Meeting 2011, held April 2-6.