Status of antiestrogen breast cancer prevention trials.

Various ongoing double-blind clinical trials are evaluating the use of tamoxifen (Nolvadex) as chemoprevention for breast cancer. A total of over 24,000 healthy women have been randomized to these trials, and it should be possible, by the year 2000, to detect any preventive effect of tamoxifen in healthy women. Furthermore, with the large numbers of women involved, it should be possible to evaluate prevention in subgroups of participants according to risk of the disease, particularly those women carrying high-risk genes, such as BRCA1 and BRCA2. Adverse effects of tamoxifen have been identified, including a transient bone loss in premenopausal women and uterine effects, including polyps, cysts, and endometrial cancer, in postmenopausal women. Although the potential benefit of tamoxifen in preventing breast cancer in healthy women is likely to outweight any potential long-term risks, the use of other tamoxifen-like drugs, such as raloxifene (Evista) and toremifene (Fareston) is now being investigated.