A new analysis of data from a study of post-menopausal women is challenging existing guidelines on hormone therapy. The researchers say women taking estrogen alone are at a significantly lower risk of breast cancer, and do not show an increased risk of blood clots or stroke, as reported in an earlier study.
Synthetic estrogen was first developed around 80 years ago and has been used to replace the natural hormone that women no longer produce after menopause. It later became routine for doctors to prescribe estrogen - alone or in combination with progesterone - to ease menopausal symptoms.
Then, in 2002, U.S. officials added estrogen to a list of substances "known" or "reasonably anticipated" to cause cancer.
That finding came from a huge U.S. research study called the Women's Health Initiative, which also challenged previous studies that suggested hormone treatment protected against heart disease and stroke.
Dr. Joseph Ragaz of Canada's University of British Columbia and colleagues have sifted through data from the Women's Health Initiative and concluded that estrogen therapy not only does not cause breast cancer, it actually may protect many women from the disease.
"Estrogen alone can be recommended for a majority of women in menopause to prevent quality of life deterioration, but also to reduce breast cancer," Ragaz says.
The researchers found a modest reduction for women who may already be at risk for breast cancer, such as those with a family history of the disease. But for the majority of women who don't have the risk factors, Ragaz says the benefit of the estrogen therapy is very substantial.
"Those women without underlying risk benefit significantly more - the figures are up to 30 to 40 percent reduction of breast cancer risks. In our final recommendation we will have to say that one shoe is not for everybody; we still have to skillfully identify the low-risk and high-risk [patients]."
Previous analysis of data from the Women's Health Initiative found a slightly lower risk of breast cancer among women taking estrogen alone, but the reduction wasn't statistically significant.
Ragaz says natural estrogen produced by a woman appears to promote cancer, but the synthetic variety used in hormone therapy seems to protect breast tissue from cancer. He admits it is unclear why this would be, and says it is not the subject of his current research.
Ragaz and his colleagues also found that women who begin estrogen therapy before age 60 show reduced risk of heart disease, colon cancer, and bone fracture. They did not find an increased risk of stroke or blood clots, which was found previously in a group that included women who began taking hormones at all ages.
However, he also said that his analysis confirms earlier findings that hormone therapy that combines estrogen with progesterone does significantly increase the risk of breast cancer.
Joseph Ragaz of the University of British Columbia presented his findings in Texas at the San Antonio Breast Cancer Symposium, co-sponsored by the American Association for Cancer Research and academic institutions.