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Study Shows Isoflavone Exposure Has Little Effect on Breast Cancer Risk or Recurrence

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Key Points

  • A review of studies examining the impact of soyfoods on breast cancer risk has found clinical evidence indicating isoflavone exposure has little effect on the markers of breast cancer risk.
  • Evidence suggests that consuming soyfoods after a breast cancer diagnosis is not harmful and can provide nutritional benefits to breast cancer survivors, especially with respect to cardiovascular disease.

According to a review of studies examining the impact of isoflavones in soyfoods on breast cancer risk, clinical evidence indicates that exposure to isoflavones, which are classified as both phytoestrogens and selective estrogen receptor modulators, has little effect on the markers of breast cancer risk. The study, published in Oncology, examined research evaluating the effects of isoflavone exposure on reproductive hormone levels, mammographic density, nipple aspirate fluid contents, and cell proliferation.

Study Details

In a review of a meta-analysis of 35 studies involving postmenopausal women, Mark Messina, PhD, MS, Professor in the Department of Nutrition at Loma Linda University, California, and colleagues reported that isoflavones had no statistically significant effects on estradiol, estrone, sex hormone binding globulin, follicle-stimulating hormone, or luteinizing hormone, although there was a small, statistically nonsignificant increase in total estradiol.

In addition to not increasing breast cancer risk, evidence also suggests that consuming soyfoods after a breast cancer diagnosis is not harmful and may provide nutritional benefits, especially for cardiovascular health, said the authors.

Recommendations

“The totality of the reviewed evidence provides no basis for advising breast cancer patients, especially postmenopausal women, against the consumption of soyfoods. However, since the epidemiologic data, but not the clinical data, are supportive of potential benefits, sufficient evidence to recommend soyfoods to breast cancer patients to improve prognosis does not exist at this time,” said the authors. “Therefore, the most justifiable position for clinicians is to allow soyfood use by patients for whom soyfoods already represent a normal part of their diet (mainly vegetarians and patients of Asian ethnicity) and not to discourage other survivors from moderate consumption. This recommendation is consistent with the position of the American Cancer Society and the American Institute for Cancer Research,” they concluded.

Dr. Messina is an advisor to the United Soybean board. The remaining study authors reported no potential conflicts of interest.

The content in this post has not been reviewed by the American Society of Clinical Oncology, Inc. (ASCO®) and does not necessarily reflect the ideas and opinions of ASCO®.


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