I've been re reading the Food Hourglass section on mushrooms. Mushrooms are apparently a really good anti cancer food. If you eat just a few mushrooms a day you dramatically reduce your risk of developing cancer. If you combine eating mushrooms with drinking green tea the cumulative effect reduces the risk further.
Just as a quick example, a woman can reduce her chances of developing breast cancer by 89% if she drinks green tea and eats a few mushrooms every day. If a tablet could be proved to do that we'd pay a fortune for it.