Figure 1.

Decision-gate agent selection and testing process. Although ideas for chemopreventive agents come from a variety of sources, most agents are suggested from preclinical data presented in peer-reviewed published articles. 1) Prevention efficacy may be suggested by epidemiologic data on cancer incidence from population studies of widely used approved drugs for nonmalignant diseases, suggesting the possibility of “repurposing” drugs to cancer prevention. 2) Nutritional components are also suggested as having preventive properties based on observational data associating specific diets or use of individual nutrients with cancer incidence. 3) Retrospective analyses of secondary cancer endpoints or even nonprospectively collected cancer data from trials of noncancer drugs also offer hypotheses regarding cancer prevention effects. 4) Prevention of second primary cancers within treatment trials of existing cancers, breast cancer being the most obvious example, also has supported the testing of treatment agents for prevention. IND = investigational new drug.