Soy and Breast Cancer Update
Written by Dr. Jen Green, Naturopathic Doctor
For nine years I’ve been wondering whether soy is safe in postmenopausal breast cancer survivors who were hormone receptor positive. The study I’ve been waiting for was finally published last month!
1,954 breast cancer survivors were followed over 6.3 years and their soy consumption was monitored along with their risk of recurrence. Postmenopausal women taking Tamoxifen who consumed the highest levels of soy had a 60% reduction in breast cancer recurrence risk compared to the lowest soy consumption group. Women who had never used tamoxifen had no apparent benefit. Women with hormone receptor negative tumors who had the highest soy intake had a non-significant trend towards increased risk of recurrence. Overall, there was a non-statistically significant trend of reduced risk with soy consumption in all women.
From my perspective, the take home messages are as follows;
Women taking tamoxifen should include liberal amounts of fermented organic soy in their diet (up to daily). Tamoxifen and soy seem to work synergistically.
We are still unsure about how Arimidex and soy interact, so moderation is advised (eg. organic fermented soy no more than a few times weekly).
Women with hormone receptor positive tumors can safely include organic fermented soy in their diet in moderation (a few times weekly). Although their may be no direct risk reduction, they do not need to be afraid of it.
Women with hormone receptor negative tumors should limit soy to no more than twice weekly.
The new burning question remains, “How does soy interact with Arimidex/the newest class of aromatase inhibitors?”. Hopefully we won’t need to wait so many years next time to find out!
Guha N, Kwan ML, Quesenberry CP Jr, Weltzien EK, Castillo AL, Caan BJ “Soy isoflavones and risk of cancer recurrence in a cohort of breast cancer survivors: the Life After Cancer Epidemiology study.”.Breast Cancer Res Treat. 2009 Feb 17