Actually I know a person who has Prostrate Cancer (non AS related) doc recomended (actually insisted) that he use Soy milk among many other soy products - I would say that its a mighty force in the battle, but it should help and is good for prevention.
Proscar (finasteride) will also help.
Prestrate cancer is a serious condition it deserves more publicity and focus than it gets, I think it has less publicity b/c males tend to keep to themselves their problems where-as with breast-cancer or the likes women are not as guarded with their communication. Thats a tangent though.