I've read many studies that Cancer is mostly caused by a deficiency of Vitamin D. Other vitamins, such as Vitamin A, Vitamin E, Vitamin C, also come into play, and probably more nutrients as well.
I, personally, supplement with Cod liver oil, Vitamin C, and take generous amounts of olive oil (for vitamin E). Not only because they prevent cancer, but also help with overall health.
Another issue is how many processed food additives thwart the absorption of these important vitamins Of particular note are the chemically made franken-foods such as olean, MSG, sugar alchohols, and aspartame which all thwart the normal absorption of cancer-preventative vital nutrients. On top of that, low-fat diets, which are recommended to everyone, are sadly depleted of these essential fat-soluble nutrients.