Last year I participated in The Women's Wellness After Cancer Program
www.wwacp.com.au and it quoted 2 studies from the American Institute for Cancer Research which indicated that eating moderate amounts of soy food (1 or 2 servings daily) is safe for breast cancer survivors. WWACP actually encouraged participants to increase their soy intake and recommended 2 serves per day as this would supposedly lead to increased health benefits eg reduced menopausal symptoms and a lower incidence of cardiovascular disease.
A serve was listed as 1 cup of soy milk, 2 slices of soy and linseed bread, 35g of soy breakfast cereal, 100g of tofu or 5g of linseeds. The benefit is only from consuming food sources not from supplements taken as powders or pills.
I felt uncomfortable with this as my oncologist had said that I didn't need to avoid soy but recommended limiting myself to 1 serve per day. I chose to follow his advice.
I have copied the links to the studies quoted - hopefully they work.
http:/www.aicr.org/cancer-research-update/2012/november_21_2012/cru-soy-safe.html
http:/www.aicr.org/foods-that-fight-cancer/soy.html#research