PHASE-III, LARGE-SCALE CHEMOPREVENTION TRIALS - APPROACH TO CHEMOPREVENTION CLINICAL-TRIALS AND PHASE-III CLINICAL-TRIAL OF TAMOXIFEN AS A CHEMOPREVENTIVE FOR BREAST-CANCER - THE US NATIONAL-CANCER-INSTITUTE EXPERIENCE

Clinical trials to evaluate interventions for cancer prevention are de signed as early (phase I, IIa, and IIb) or late-phase studies. Whereas the former are small and generally rely on intermediate endpoint biom arkers of carcinogenesis, the latter are large-scale, longterm, random ized, phase III studies that address endpoints such as cancer incidenc e. The Breast Cancer Prevention Trial, P-1, conducted by the National Surgical Adjuvant Breast and Bowel Project (NSABP), is discussed as an example of a large, extended, phase III trial designed to answer the question of whether tamoxifen reduces the incidence of breast cancer i n women who ape at increased risk for the disease.