Foods. From the "lower-cancer-risk" low fat, high anti-oxidant diet in its more extreme interpretations to raw foods....
I.e., to use food as medicine.
Now, I am inclined to not view food as medicine. But you've heard it: no animal protein, no cooked animal protein, no cooked animal or vegetable protein... no yeast, yeast cakes, etc.
The true question, then, is that even though very thorough and complete diet different from the (commercial, popular standard) makes no significant change / improvement in testable outcomes of health, where cancer is concerned, it may, in populations with cancer, make subtle but important changes.