Women’s Health Initiative
In May 2002, the Women’s Health Initiative (WHI) halted a study of combination estrogen-progestin therapy in post-menopausal women after researcher found that it increased the risk of side effects from hormone replacement therapy.
Although the study was scheduled to run until 2005, the researchers chose to halt it because they felt that the dangers of hormone replacement therapy outweighed its potential health benefits.
Purpose of the study
The WHI hormone replacement therapy study was intended to examine the benefits of estrogen and progestin on post-menopausal women who had not had a hysterectomy. The study found that estrogen and progestin increased the risk of heart attack, blood clots and breast cancer.
M.D. Anderson’s confirmation
The WHI’s conclusions about the link between HRT and breast cancer were confirmed in December 2006 in a study by the University of Texas M.D. Anderson Cancer Center. Following the WHI’s announcement of the risk of hormone replacement therapy side effects in 2002, many women stopped taking estrogen and progestin in order to avoid the possibility of developing breast cancer, heart disease, blood clots or stroke.
The M.D. Anderson study found that in 2003—the year after this announcement—breast cancer rates fell by an astounding 7% among all women. This was the first drop in new breast cancer cases that had been observed in decades.
Although scientists cautioned that their results did not definitively prove that the drop in breast cancer cases was caused by the lower number of HRT patients, they said that nothing else seemed to be able to explain such a significant drop.