Chemoprevention of cancer: implications for clinical pharmacology

Chemoprevention of cancer

Chemoprevention is a strategy used to block the development of cancers in human beings. This emerging field has broad potential for influencing cancer incidence rates in defined high-risk groups and the general population. In this review, we define some of the mechanisms of carcinogenesis, describe some of the genetic markers of carcinogenesis, and list possible biomarkers that may serve as surrogate end points in chemoprevention studies. A major component of this review is a description of the agents that are currently under investigation in animal systems or in human trials. They are grouped according to the agents that block or suppress mutation, such as oltipraz, selenium, vitamin C and the flavones, or according to agents that block promotion and proliferation, such as difluoromethylornithine, tamoxifen, nonsteroidal antiinflammatory drugs, and the vitamin A derivatives. We describe the issues that are considered in the design of chemoprevention trials and in the phase I, II, and III components of these trials. The following national trials are discussed: the Breast Cancer Prevention Trial, which uses tamoxifen; the Prostate Cancer Prevention Trial, which uses finasteride; and a Lung Cancer Prevention Trial, which uses 13-cis-retinoic acid. The review ends with some insights about future studies in chemoprevention.

Time-related factors in research on diet and cancer

Time-related factors have been an integral aspect of laboratory and epidemiologic studies concerning the effects of diet on cancer. In this survey, we illustrate several ways in which consideration of time factors has furthered our understanding in this area. As one of the key dimensions in descriptive studies of secular trends and migrant populations, time factors suggest general associations between diet and cancer. The investigation of time-related parameters such as age, duration of dietary exposure, and time from exposure to cancer, lends greater specificity to the diet-cancer relationship. Both micro- and macro-nutrients are examined, as well as nutrition-mediated factors such as growth and anthropometry. Time-related issues relevant to the design of future observational and intervention studies of diet and cancer (i.e. critical etiologic periods, timing of dietary assessment, biological indicators, and secular trends) are also discussed.