Estrogen Replacement Therapy May Not Increase Women's Risk of Breast Cancer
While several widely reported studies over the past few years have shown an increased risk of breast cancer among post-menopausal women who take hormone replacement therapy, results of a recent study find that this may not be the case in all circumstances. In an updated analysis of findings from the U.S. government-sponsored Women's Health Initiative study, researchers found that post-menopausal who took estrogen-alone replacement therapy did not increase their risk of breast cancer. The results contradict the group's previous Estrogen plus Progestin Trial, which found an increase in breast cancer over about 5 years among women taking combined hormone therapy (estrogen plus progestin).
Hormone replacement therapy (HRT) is a drug treatment consisting of synthetic estrogen and/or progesterone (progestin) designed to "replace" a woman's depleting hormone levels and relieve menopausal symptoms such as hot flashes and vaginal dryness. About 60% of menopausal women experience hot flashes, which may be accompanied by sweating, flushing, or heart palpitations.
Past research has shown that HRT may help prevent osteoporosis, heart disease short-term memory loss, depression and other diseases in post-menopausal women. However, recent research has found that HRT may not provide these benefits and may pose other risks, including an increased risk of breast cancer, ovarian cancer (with long-term use) and cancer of the uterine lining (in women do not take progestin with estrogen). In July 2002, the National Institutes of Health halted a large study on HRT, called the Women's Health Initiative, because the combined estrogen/progestin regimen of the therapy was found to cause 8 cases of invasive breast cancer for every 10,000 women on HRT (a 26 percent increase in breast cancer risk compared to women who do not take HRT).
Women who have not had their uteruses removed must take progestin with estrogen to counter the increased risk of endometrial cancer (cancer of the uterine lining) that can occur with HRT. However, women who have had a hysterectomy (about 25% of menopausal women) have the option of taking estrogen-alone therapy to relieve menopausal symptoms.
In the latest study, researchers now say that estrogen-alone replacement therapy may not increase the risk of breast cancer. "What is clear now is that, overall, post-menopausal women without a uterus who choose to take estrogen-alone do not have an increased breast cancer risk, at least over the first 7 years of treatment," said study author Marcia Stefanick, PhD of Stanford University, in a Women's Health Initiative news release. "This is clinically relevant, but women who are taking estrogen should also be aware that they will likely need more repeat mammograms and more breast biopsies," she said.
To conduct the study, researchers had 5,310 women take active estrogen (0.625 mg/day of conjugated equine estrogens) and 5,429 women take a placebo (an inactive pill). According to the Women's Health Initiative, about 35% of the women had used hormone therapy prior to the study and about 13% were using hormones at the time they enrolled, but they had to be off of hormones for at least 3 months prior to starting the trial.
The study found that:
- Over an average of 7 years of follow-up, women taking estrogen had fewer breast cancer tumors than those women who took a placebo.
- Women who took estrogen were diagnosed with breast cancer at a rate of 28 per 10,000 per year versus a rate of 34 per 10,000 per year among women taking a placebo.
- The difference in rates of breast cancer (6 per 10,000) between the groups was not statistically significant, meaning it could have occurred by chance.
Source: Women's Health Initiative Estrogen-Alone Trial
The study also found that women who took estrogen were 50% more likely to have abnormal mammograms that required follow-up. Abnormal mammograms suggest the presence of cancer. Similarly, among the women who took estrogen, there were 33% more breast biopsies than among the women who did not take estrogen. Breast biopsies prove or disprove the presence of breast cancer. However, an abnormal mammogram and/or breast biopsy does not necessarily mean that women have breast cancer.
"Longer follow-up is needed to fully explain the reduced number of breast cancers in women taking estrogen," said National Heart. Lung, and Blood Institute Director and Women's Health Initiative Director Elizabeth G. Nabel, MD, in a news release. "However, this new analysis does not alter the overall conclusion from the Women's Health Initiative that hormones, including estrogen-alone and estrogen plus progestin, should not be used for the prevention of chronic disease. The findings still support current recommendations that hormone therapy should only be used to treat menopausal symptoms and should be used at the smallest effective dose for the shortest possible time."
Researchers say that more studies are needed, particularly on the role of progestin. Hormone replacement therapy remains controversial. For some women, the benefits of relieving severe menopausal symptoms may outweigh the potential risks, but for other women, the risks may outweigh the benefits. At the moment, the best advice experts can give is for women to discuss the benefits and risks of HRT with their physicians and make informed choices.