Consuming soyfoods may reduce the recurrence of breast cancer, according to a recent study.

Although women with breast cancer are often told not to eat soyfoods or soy-based supplements because of how they may adversely affect anti-estrogen treatment, researchers at Georgetown University found that eating these type of foods may boost the immune system.

"I am concerned that some patients may start taking soy supplements when they shouldn't and that others will stop eating soyfoods when they could really benefit from them," Leena Hilakivi-Clarke, lead investigator of the study, said in a statement.

The belief that soy can stimulate the growth of breast cancer cells and disrupt anti-estrogen treatment stems from mice studies that use mice that do not have immune cells known as cytotoxic T cells, known to attack breast cancer. This led scientists to advise their breast cancer patients not to eat soyfoods.

In a previous study conducted by Hilakivi Clarke and Xiyuan Zhang, the lead author of the current study, confirmed that rats that consumed genistein, an isoflavone found in soybeans, fava beans and soymilk, among other soy foods, throughout their lifetimes responded better to anti-estrogen treatment than did control rats.

In the current study, researchers investigated if their previous findings could be explained by changes in tumor immune responses. While T cells can attack tumor cells, other immune cells can disable the ability of these T cells to recognize that tumors are present, allowing breast cancer to grow unchecked by the immune system.

They found that in rats fed genistein since before puberty, the T cell immune response was activated already before they started treatment with tamoxifen (an anti-estrogen therapy). Also, during the treatment, the tumor's attempt to hide from an immune system attack was thwarted.

"Our results suggest that genistein's ability to activate anti-tumor immune responses and reduce expression of immunosuppressive mechanisms may explain why lifetime genistein intake reduces risk of breast cancer recurrence," Hilakivi-Clarke said.

Zhang said it is critical that "genistein is consumed well before a tumor develops to program the tumor to exhibit good immune responses."

The findings, which will be presented at the American Association for Cancer Research (AACR) Annual Meeting 2015, could impact the advice women diagnosed with breast cancer are given.