Clinical trials in cancer prevention.

Research in cancer prevention can be divided into laboratory research, epidemiologic research, and clinical trials. When results from laboratory and/or epidemiologic research support the possibility of clinical cancer prevention, these leads should be subjected to study in clinical trials. If clinical trials produce positive results, wide application of these results to the relevant segments of the general population should then be emphasized. Why are clinical trials needed in cancer prevention? There are several considerations: epidemiologic studies may lack specificity, that is, the ability to reach conclusions that apply to only one specific factor; the predictive value of animal models based on laboratory studies is not entirely known; clinical trials quantitate the level of participant acceptance of the intervention; and clinical trials address the issues of risk/benefit ratios. Over the last 3 years, the National Cancer Institute has supported the development of a program of clinical trials in cancer prevention. The aim of these studies includes the reversal of precursor lesions, prevention of progression from a precursor state to overt malignancy, reduction in the incidence of malignancy, reduction in cancer mortality, and reduction in overall mortality. Interventions under study include a diet with less than 20% of calories from fat, and the administration of single agents or combinations of agents, including beta carotene, vitamin A, 13-cis-retinoic acid, vitamins C, E, and B12, and folacin.