How does postmenopausal hormone use affect breast cancer risk and survival?
The estrogen and progestin component of the Women’s Health Initiative concluded definitively in 2002 that combined estrogen and progestin therapy increases the risk of invasive breast cancer. After an average of five years of follow-up for each of more than 16,000 women in the study, the study found a 26 percent increase in breast cancer risk as compared to women taking placebo (106). After five years of follow-up, the WHI study had found no indication of an increased incidence of breast cancer in the group of 11,000 trial participants taking estrogen alone (106). This clinical trial of estrogen vs. placebo is continuing. Observational studies, however, do indicate an increase in risk among women taking estrogen alone. A recent re-analysis of over 90 percent of breast cancer studies throughout the world showed an increased risk in breast cancer for women who used postmenopausal hormones for five years or longer. Most of the women included in this re-analysis were on estrogen alone. In
