Hi Shelley,
If you check the news section of the OCF site, there are a number of articles listed that deal with this topic.

In addition to the usual recommendations to eat lots of fruit and vegetables, it seems that green tea and tumeric (or its active ingedient, circumin) are both promising in their potential to fight cancer, although clinical trials and data are scarce. There are also some articles on Vitamin E and other anti-oxidants.

Hope this is of some help. - Sheldon