Public Release:  Soy isoflavone supplements did not provide breast cancer protections

American Association for Cancer Research

PHILADELPHIA -- Soy isoflavone supplements did not decrease breast cancer cell proliferation in a randomized clinical trial, according to a study published in Cancer Prevention Research, a journal of the American Association for Cancer Research.

Lead researcher Seema A. Khan, M.D., professor of surgery at the Robert H. Lurie Comprehensive Cancer Center of Northwestern University, said the results of this study are consistent with the findings of previous studies that were designed to test cancer prevention benefits of dietary supplements.

"Simply put, supplements are not food. Although soy-based foods appear to have a protective effect, we are not seeing the same effect with supplementation using isolated components of soy, so the continued testing of soy supplements is likely not worthwhile," said Khan.

Khan said that beta-carotene and selenium supplementation have also been shown to lack benefit in lung cancer prevention studies.

"Foods are very complex and there are likely traveling companions that we haven't identified that are protecting against cancer," said Khan.

For the current study, Khan and colleagues randomly assigned 98 women to receive a mixed soy isoflavones supplement or placebo. Isoflavones are components of soy foods that were expected to have anti-estrogen activity.

These women had more than 4,000 breast cancer epithelial cells identified by fine needle aspiration biopsy. At six months, researchers evaluated the levels of Ki-67, an established protein marker of cancer cell growth. In the overall population, no difference was seen after six months in either group. However, among pre-menopausal women, the level of Ki-67 increased from 1.71 to 2.18, suggesting a negative effect of the supplementation.

"This was a small finding, but one that should suggest caution," said Khan.

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About the AACR

Founded in 1907, the American Association for Cancer Research (AACR) is the world's first and largest professional organization dedicated to advancing cancer research and its mission to prevent and cure cancer. AACR's membership includes 34,000 laboratory, translational and clinical researchers; population scientists; other health care professionals; and cancer advocates residing in more than 90 countries. The AACR marshals the full spectrum of expertise of the cancer community to accelerate progress in the prevention, diagnosis and treatment of cancer through more than 20 conferences and educational workshops, the largest of which is the AACR Annual Meeting with more than 18,000 attendees. In addition, the AACR publishes seven peer-reviewed scientific journals and a magazine for cancer survivors, patients and their caregivers. The AACR funds meritorious research directly as well as in cooperation with numerous organizations. As the scientific partner of Stand Up To Cancer, the AACR provides expert peer review and scientific oversight of individual and team science grants in cancer research. The AACR actively communicates with legislators and policymakers about the value of cancer research and of related biomedical science in saving lives from cancer.

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