There is a 30% lower risk of developing breast cancer among women in Asian countries who are known for their high soya intake (compared to American women). Also, there is a 21% reduction in mortality among women with breast cancer who consumed more soya.
It is not certain why soya protects against cancer risk. It could be because its isoflavones can increase apoptosis (a genetically programmed mechanism that tells cells to self-destruct when they get DNA damage they’re not able to repair). Without this process, damaged cells can turn into cancer.