Women's health initiative studies of postmenopausal breast cancer

The WHI has provided randomized controlled trial data on interventions that are among the most important in relation to the health benefits and risks among postmenopausal women in the USA. Postmenopausal hormone therapy did not yield the anticipated major reduction in coronary heart disease, and was responsible for both stroke elevations and fracture reductions over average 5.6 (E + P) and 7.1 (E-alone) years intervention periods. BC hazard ratios for both E + P and E-alone were about as anticipated, based on preceding observational studies, among women who had used postmenopausal hormones prior to WHI enrollment, but were lower than expected among women without such prior exposures. Whether these lower hazard ratios reflect upward bias in the observational studies or detection lags among women who tended to be quite a few years from menopause when randomized in the WHI trials remains to be fully clarified. At any rate, E + P is associated with an elevated BC risk, while the effects of E-alone remain somewhat uncertain. The WHI DM trial is taking place among women having baseline % energy from fat around 35, in contrast to the 38-39% projected. This has led to a smaller than anticipated intervention vs. control group difference in dietary habits, and to projected and realized BC incidence rates that were about 9% lower in the intervention vs. the control group. The likelihood that this lower rate reflects a meaningful reduction in BC risk is enhanced by a lower BC hazard ratio among the 50% of women who started relatively higher in percent energy from fat, and by cohort studies, including that among women in the DM control group, showing clear positive trends between food record percent energy from fat and BC incidence.