Results from a recent study revealed that in animals, a long history of eating soy foods enhances the immune response against breast tumors, reducing cancer recurrence, contrasting with the notion that in women with breast cancer, eating soy foods or soy-based supplements can interfere with anti-estrogen treatment.
The study, which may offer good news to women who regularly consume soy foods as part of their diet, was conducted at the Georgetown Lombardi Comprehensive Cancer Center and will be presented at the 2015 Annual Meeting of the American Association for Cancer Research (AACR),
“I am concerned that some patients may start taking soy supplements when they shouldn’t and that others will stop eating soy foods when they could really benefit from them,” said the study’s lead investigator, Leena Hilakivi-Clarke, PhD, professor of oncology at Georgetown Lombardi in a recent news release.
Studies in mice that lack cytotoxic T cells, known to attack breast cancer, have shown that soy, precisely genistein (an isoflavone) can incite breast cancer cells to grow and interrupt anti-estrogen treatment, which led oncologists to advise their patients not to eat soy foods.
Hilakivi-Clarke and Xiyuan Zhang, doctoral student and lead author of the current study, determined in previous research that mice that consumed genistein during their lifetimes responded better to anti-estrogen treatment when compared to control mice. These mice also had a reduced risk of cancer recurrence. Genistein, found in all soy-derived foods, have been found to have biological effects that can reduce the risk of cancer. Nevertheless, genistein has also been found to activate human estrogen receptors, which can make existing cancer cells to grow.
In the current study, the team of researchers examined if their previous results could be justified by modifications in tumor immune responses. It is known that T-cells can attack tumor cells, however, other immune can restrict T cells ability to recognize the presence of tumors, allowing the growth of breast cancer without the immune system checking.
In mice fed with genistein since before puberty, the researchers observed that the immune system T-cell response was initiated already before they commenced tamoxifen treatment. During the treatment the researchers also observed that the tumor’s attempt to hide from an immune system attack was prevented.
“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 in the news release.
“But it is critical that genistein is consumed well before a tumor develops to program the tumor to exhibit good immune responses,” Zhang added.
Results from this study corroborate previous observations studies that revealed that women who consumed more than 10 mg isoflavones per day have reduced risk of breast cancer recurrence, in comparison to women who consume less than 4 mg isoflavones per day. “One cup of soy milk has about 30 mg isoflavones, the majority of which is genistein,” Hilakivi-Clarke said.
“This and our earlier work suggests it is okay to continue consuming soy foods during breast cancer treatment. Whether this is because of our finding related to the immune, we can’t say conclusively,” Hilakivi-Clarke concluded.