Soy in breast cancer, safe or dangerous?
Cary Presant, MD, Oncology, Hematology/Oncology, 06:50PM Dec 3, 2012

I am always asked by patients at high risk of breast cancer whether they should avoid soy because it contains phytoestrogens.  Patients are fearful of increasing their risk of breast cancer.  In fact, women who have had primary therapy for breast cancer also ask if they should avoid soy phytoestrogens.

An excellent review was published in the ASCO Post on July 15, 2012 by Barrie Cassileth. As head of the Integrative Medicine Service at Memorial Sloan-Kettering Cancer Center in New York, Dr. Cassileth has been a leader in evaluation of complementary and alternative treatments. If you ever have the opportunity to talk with her, she is full of great suggestions. Her review of the use of soy contained important information.  

Overall, she concluded that the epidemiologic evidence favored prevention of breast cancer by use of soy. Asian women typically have daily consumptions between 26 and 54 mg of soy isoflavones, and this may account for their low frequency of breast cancer.  

Most surprising was her review of epidemiologic studies suggesting that taking soy early in life through puberty was associated with a reduced risk of breast cancer.  This may be important for our patients to share with their daughters and sisters, since they can influence their intake of soy products during adolescent years and young adult years.  

Following diagnosis of breast cancer, Dr. Cassileth also concluded that soy consumption is safe. In fact, data suggests that taking soy at levels equivalent to Asian populations might reduce recurrence rates.

The American Cancer Society in April concluded that for breast cancer survivors, evidence does not suggest any adverse effects of soy products. Furthermore, a study in May indicated that in over 9,000 American and Chinese breast cancer survivors, there was a reduced risk of cancer recurrence in patients who consumed at least up to 10 mg of soy isoflavones or 3 grams of soy protein per day (S. Nechuta and coworkers, American Journal of Clinical Nutrition 96:123-132, 2012).

In my practice, I advise women that not only is soy safe, but that they should consider increasing their intake of soy products in order to make use of the potential benefits of reduction of diagnosis of breast cancer and reduction of recurrence of breast cancer.