The Soy - Breast Cancer Controversy - Cancerwise | Cancer blog from M. D. Anderson Cancer Center

"These studies provide further information that regular dietary soy as part of a normal diet is probably safe and, in fact, may be beneficial for women with breast cancer. These studies, as well as others, create a growing body of evidence that the current advice that all soy foods should be removed from the diet of a woman diagnosed with breast cancer is probably untrue.
The role of non-dietary soy products such as soy supplements, powders or pills and the use of heavily processed soy items such as soy cheese, soy hot dogs or soy turkey remain unclear and should be avoided.
As the research to date is observational in nature, future randomized trials are needed to verify if a beneficial effect truly exists for the use of dietary soy."