The chemoprevention of cancer: directions for the future.

Current Status The decade ofthe 1990s is witnessing an endorsement of the science of preventing cancer by chemical means. This represents a significant departure from the emphasis on therapeutic strategies which characterized research efforts in the 1970s and 1980s. Already more than 1 00,000 subjects have been involved in chemoprevention trials, and in 1992 the NSABP1 launched the largest nationwide chemoprevention trial ever designed, the BCPT, using the drug tamoxifen to prevent breast cancer in healthy high risk women. An even larger study involving 1 8,000 men to prevent prostate cancer is in the final planning stages. As is always the case with new scientific advances, there are historical reasons that chemoprevention is being embraced and supported by national health care policy makers at the current time. With the development of more sophisticated biochemical and technological tools, and advances in the molecular genetics of cancer, scientists have gained a more precise understanding of the process of carcinogenesis and are identifying early, potentially modifiable premalignant biochemical changes. At the same time, epidemiological studies have provided an appreciation of the role of dietary micronutrients in cancer risk and their potential for inhibitingthe progression ofprecancerous lesions. Just as important as the progress made at the biological level is the experience of limited success in finding curative therapeutic strategies for cancer, with a subsequent shift in focus to a search for preventive approaches. In view of the limited cancer research budget and the national health care crisis, much forethought and planning should accompany our chemoprevention program so as to minimize the costs and maximize the information obtained. The clinical trial experience of the last 20 years has taught us many valuable lessons which can be used in the design and implementation of chemoprevention trials. However, chemoprevention studies have several unique features which distinguish them from therapeutic trials and call for new strategies and approaches. We are at a crucial point in time for reflection on the key questions which pertain to the future of the chemoprevention of cancer.