Soy has been accused to cause breast cancer and this is just not true. In fact, consuming soy that is Non GMO and minimally processed may reduce the risk of breast cancer. Studies show that a lifelong diet rich in soy foods reduces the risk of breast cancer in women.
Soy is high in isoflavones, estrogen-like substances linked to the prevention of cancer Studies show that there is no link with Isoflavones and breast cancer (see reference below).
It was once thought that eating soy foods increase the risk of breast cancer. However, eating a moderate amount of soy foods does not increase risk of breast cancer, or other types of cancer. A moderate amount is one to two servings a day of whole soy foods, such as tofu, soy milk and edamame.
In Japan they have hardly any incidents of breast cancer because they have a diet rich in soy. They eat tofu even for breakfast.
Reference: Study of association between soy isoflavone intake and breast cancer risk for pre and post menopausal women. A Meta-Analysis of Epidomiologiacal Studies.