Ten years ago, the medical world was rocked by the discovery that estrogen-progestin hormone-replacement therapy increased the risk of breast cancer and other diseases in post-menopausal women. Hundreds of thousands of women came off HRT and within a few years we saw the first-ever documented decrease in breast cancer rates.
The discovery was made by the government-funded Women's Health Initiative, a study designed to explore the benefits and risks of combined estrogen-progestin HRT in post-menopausal women. The study was halted in 2002 when researchers saw a 26 percent increase in the relative risk of breast cancer in women taking the combined estrogen-progestin HRT compared with those taking a placebo. There were also significant increases in the risk of heart disease, stroke and blood clots.
A follow-up study done three years later showed increases in invasive cancers in women who had been on HRT. But while breast cancer rates remained elevated in this group, there was a trend towards lower rates similar to those in the placebo group, suggesting that the increased risk for breast cancer from combined HRT is reversible within a fairly short period.
As we look at other chemical exposures linked to breast cancer, the WHI study and the resulting drop in breast cancer incidence should give us great hope. The study showed us that by eliminating an avoidable exposure to chemicals we can reduce breast cancer risk. It gave us a tangible example of why we do the work we do—why we work every day to reduce our exposure to toxic chemicals and radiation linked to the disease. So on this 10th anniversary, we are thankful to the researchers and women who were part of the study. Because of their contribution, millions of women now have clear information about the risks of estrogen-progestin HRT, and all of us working to prevent breast cancer have a case study for why we must continue to call for more research on the causes of breast cancer and for action—by individuals, corporations and government—to prevent exposure to toxic chemicals and radiation linked to the disease.