Isoflavone Research Initiative

The most recent findings on soy and isoflavones were presented in Washington DC on the occasion of the 9^th International Symposium on the Role of Soy in Health Promotion and Chronic Disease Prevention and Treatment (October 16-19, 2010). A major part of the topics was dedicated to safety and health benefits in menopausal women, and to the issue of soy and breast cancer.

Dr. Xinmei Kang (Harbin Medical University, China) reported on clinical data obtained in breast cancer patients post surgery (Kang et al. 2010a). In this recently published trial (Kang et al. 2010b) she observed the association between dietary soy isoflavone intake and breast cancer recurrence and survival among 524 post-operative breast cancer patients receiving adjuvant endocrine therapy. 85 % of the breast cancer patients were ER(+) and/or PR(+). The median follow-up time was 5.1 years.

Pre-menopausal patients had an overall survival rate of 69.4 %. The comparison of patients in the lowest quartile of isoflavone intake (< 15.2 mg/day) and patients in the highest quartile (42.3 mg/day) did not give a correlation of isoflavone intake and overall mortality (HR 1.05, 95 % CU 0.78-1.71; p = 0.87). However, this lack of a correlation also means that isoflavones do not increase the mortality of high risk breast cancer patients.

In contrast, isoflavone exposure was clearly associated with a statistically significant reduction of the risk of breast cancer recurrence. The most important effect size was found in the group postmenopausal women (HR 0.67, 95 % CI 0.54-0.85, p = 0.02), and thus explicitly in the group where the hypothesis claims a higher risk of isoflavones. The inverse association with the risk of recurrence was also observed in patients with ER(+)/PR(+) disease and in patients treated with anastrozole.

The study results contradict the hypothesis of an increased breast cancer risk in menopausal women. They point to potential synergism of isoflavone effects with the efficacy of cancer drugs such as anastrozole.

References

Kang X, Zhang Q, Wang S, Huang X and Jin S (2010a). Association between soy isoflavone intake and breast cancer recurrence and survival among postoperative patients receiving adjuvant endocrine therapy. 9^th International Symposium on the Role of Soy in Health Promotion and Chronic Disease Prevention and Treatment, Washington DC, 16-19 October.

Kang X, Zhang Q, Wang S, Huang X and Jin S (2010b). Effect of soy isoflavones on breast cancer recurrence and death for patients receiving adjuvant endocrine therapy. CMAJ DOI:10.1503/cmaj.091298.