An evidence-based approach to cancer prevention clinical trials.

Research on carcinogenesis and its inhibition has made significant progress in the last 30 years, providing an impressive body of evidence that supports various strategies for cancer prevention. Innovative studies have helped to identify potential causes of cancer, including environmental factors such as diet, and provided valuable information about their mechanisms of action. Hundreds of epidemiologic and experimental studies have focused on possible associations between dietary factors and different types of cancer. During the same period, potential inhibitors of cancer that appeared able to prevent, arrest or reverse cancer development by interfering with one or more steps in the process of carcinogenesis were identified, and the term 'chemoprevention' was coined for this pharmacological approach to cancer prevention. Promising compounds were systematically evaluated for their potential as chemopreventive agents. Numerous agents were determined to be safe and effective in preclinical trials, including naturally occurring vitamins, minerals and phytochemicals as well as synthetic compounds. Based on preclinical results, selected agents have been and are now being evaluated in phase I, II and III clinical interventions for various cancers. Development of valid surrogate end point biomarkers for clinical disease that can be modulated by interventions is essential to accelerate progress in cancer prevention clinical trials.