Cancer prevention: epidemiology and experiment.

Perhaps the most promising lead to the prevention of cancer is derived from the epidemiologic observations that vegetables and fruit are consistently associated with lower risk of cancers of most epithelia. Over 200 studies have been undertaken, and a high proportion of them show lower risk with greater consumption. There are many plausible pathways to explain this risk reduction. The initial human experiments with specific single agents have proved to be disappointing. Single agents are not an advocated approach to chemotherapy, and may be inappropriate for chemoprevention. Foods may provide the optimal mix of phytochemicals and the best polypharmacy against the emergence of malignant clones.