Salmon is a kind of oily fish that contains a good amount of omega-3 fatty acids which slows down the growth of cancerous tumors and also boosts the immune system. At the same time salmon is also a smart lean protein source along with vitamins B12 and D. All these elements provide your body with the nutrients required to regulate cell growth and prevent cancer. You can eat salmon by steaming it, baking it or grilling it. For better result try to eat three portions of fresh salmon each week. Along with salmon, other oily fishes that can prevent breast cancer are mackerel, sardines, trout, sea bass and tuna.