Cancer chemoprevention.

A new direction for cancer prevention and control is chemoprevention, defined as the use of specific natural and synthetic chemical agents to reverse or suppress carcinogenesis and prevent the development of invasive cancer. The chemopreventive approach depends on the ability of certain chemical agents to block mutagenesis and control cellular differentiation and proliferation in epithelial tissues. Support for the chemopreventive approach is based on the biologic concepts of field cancerization and multistep carcinogenesis, as well as the clinical efficacy already shown by agents such as retinoids and tamoxifen in reversing premalignancy and preventing second primary tumors. Although chemoprevention is not yet established as a standard therapy, the results of reported trials are very promising and have raised tremendous interest in this strategy for cancer prevention. The development of more effective, less toxic chemopreventive agents remains a high priority in furthering the use of this clinically valuable approach to the prevention and control of cancer.