Primary cancer prevention has mainly two 1000 aspects in its methodology: (1) exclusion or avoidance of the environmental carcinogens or other chemical factors closely relating to carcinogenesis such as tumour promoters; and (2) the administration of inhibitory or suppressive agents against carcinogenesis. Because the number of critical agents in cancer is almost untold, continuous exposure to such agents should be inevitable in daily life. Therefore, it has been widely accepted that the latter aggressive approach, direct chemical inhibition or suppression, should be rather efficient for the control of cancer incidence. Particularly, food phytochemicals could be important for cancer prevention. In fact, a great number of epidemiological studies of the relationship between food and cancer, together with the research in the experimental animal models, have demonstrated that daily ingestion of some vegetables and fruits could undoubtedly contribute to cancer prevention1-4.
Cancer chemoprevention is a concept defined as the prevention of cancer by the administration of natural or synthesized pure chemicals, or by daily foods enriched with cancer preventive components5-8. As an initial step to human intervention trials, the target populations for cancer chemoprevention are generally recognized as so-called high-risk segments such as: (1) individuals in contact with certain carcinogens occupationally; (2) survivors from primary cancer with high possibility of recurrence; (3) individuals with a genetic history of a high frequency of cancer incidence; (4) individuals with predicted premalignancy by diagnosis with biomarkers; and (5) certain others. Though still controversial, cancer preventive agents may also be applicable to healthy people in the near future. In any case, because an infallible remedy for cancer has not been established yet, cancer chemoprevention may become a means to reduce cancer incidence.