Should women be advised to take prophylactic endocrine treatment outside of a clinical trial setting?

Epidemiological, experimental and clinical data strongly support the possibility that breast cancer can be prevented by using anti-estrogenic interventions in healthy women. Four trials involving over 25,000 women have so far been reported using tamoxifen 20 mg/day or placebo in healthy women to chemoprevent breast cancer, and several trials utilizing raloxifene or aromatase inhibitors are underway. Interim analyses of the Royal Marsden tamoxifen trial and the Italian national trial showed no effect on the early incidence of breast cancer. The NSABP-P1 showed a 49% reduction in early incidence of breast cancer. This was associated with a reduction in osteoporotic fractures but increases in the risks of endometrial cancer, cataract and thromboembolism. The IBIS trial showed a 32% reduction with a two-fold increase in endometrial cancer and in thromboembolic events. Mortality rates of breast cancer in women receiving tamoxifen prophylactically should be monitored and further follow-up of these trials is needed to determine whether tamoxifen provides an overall health benefit or increase specific or overall survival of breast cancer. High-risk women should not be advised to take anti-estrogens outside of a clinical trial setting.