Cancer chemoprevention: a summary of the current evidence.

Cancer chemoprevention is defined as the use of natural, synthetic, or biological chemical agents to reverse, suppress, or prevent either the initial phase of carcinogenesis or the progression of neoplastic cells to cancer. At present, the circle of agents with an established chemopreventive effect is restricted to tamoxifen and raloxifene in breast cancer, finasteride in prostate cancer, and celecoxib in colon polyp prevention. However, in recent years, there has been an exponential increase in the study of agents that have a chemopreventive potential against cancer. In this review, the current evidence regarding cancer chemoprevention in major target organs is summarised, discussing the epidemiological as well as the experimental data.