Chemoprevention of breast cancer, a dream? In one American study (National Surgical Adjuvant Breast and Bowel Project, NSABP-P1) tamoxifen decreased the incidence of invasive and non-invasive breast cancer, whereas in two English and Italian studies, it did not reduce this risk. Differences in the study population for the trials may underly these conflicting findings. New drugs, the SERMs, may be more promising.