But experts say that response probably wasn’t warranted. They say many women can safely take hormones for a short time to quell bad hot flashes, night sweats, and mood swings that can accompany menopause.
“The effects on breast cancer are so different between estrogen and progestin and estrogen alone that we felt it was time to say that women taking estrogen alone may not need to stop at three to five years. Because over that amount of time, no breast cancer showed up in women taking estrogen alone,” says Gass, who is also a co-author on the new study.
Estrogen and progestin are typically prescribed together when a woman still has her uterus to reduce the risk of uterine cancer while promoting the benefits of estrogen therapy.
Yet estrogen alone is used in women who've had a hysterectomy, or removal of the uterus. Statistics show about one-third of women in the U.S. have had a hysterectomy by the time they are 60.
Findings ‘Clearly Very Reassuring’
For the latest study, which is published in The Lancet Oncology, researchers kept tabs on more than 7,600 women who took part in the estrogen-only treatment arm of the trial.
The women assigned to get estrogen took that hormone for about six years before they stopped. They have now been followed for nearly five years beyond their estrogen use.
Compared to women taking a placebo, women who took estrogen had a 23% reduced risk of invasive breast cancer. That means 151 women got breast cancer in the estrogen group compared to 199 women assigned to the placebo.
Women taking estrogen also had a 63% reduced risk of dying from breast cancer compared to women on the placebo. Overall, there were six deaths in the estrogen group compared to 16 in the placebo group.
In an email, Anthony Howell, MD, a professor of medical oncology at the University of Manchester in the U.K., says the study findings are “clearly very reassuring for women.”
"However, they have to be counselled concerning the very small increased risk of deep vein thrombosis [blood clot in a vein] and pulmonary embolism [blockage of blood to the lungs], which is seen with any hormones such as the oral contraceptive pill," says Howell, who wrote a comment on the findings but was not involved in the research.
Breast Cancer Benefit May Not Apply to All
Several other important warnings also apply.
The first is that estrogen did not appear to help some women. Those were women at higher risk for breast cancer because they had a family history or history of having benign breast disease. Estrogen may even increase the risk of breast cancer in women who already have other risk factors.
“For women who are most in need of a breast cancer reduction strategy, this approach isn’t going to work,” says researcher Garnet L. Anderson, MD, principle investigator of the Women’s Health Initiative Clinical Coordinating Center in Seattle.
"These agents should not be used for breast cancer prevention, even though we clearly show a lower risk of breast cancer in these women taking hormones," says Anderson, who is also a member of the Fred Hutchinson Cancer Research Center.
The second important consideration is that the study tested a kind of estrogen called conjugated equine estrogen, which is sold under the brand name Premarin. In recent years, that formulation has become less popular. More women have moved toward using estradiol, which is chemically closer to the body's own estrogen. But researchers say they aren't sure if the two kinds of estrogen work the same way.
“Conjugated equine estrogens are very complex pills,” Anderson says. “There are a lot of different estrogen compounds in them. We really don’t know what the active agents are. To make a leap to another form is really hard to say.”
SOURCES:Anderson, G. The Lancet Oncology, March 6, 2012.Howell. A. The Lancet Oncology, March 6, 2012.LaCroix, A. Journal of the American Medical Association, April 6, 2011.Jungheim, E. Journal of the American Medical Association, April 6, 2011.Garnet L. Anderson, MD, principle investigator, Women’s Health Initiative Clinical Coordinating Center; member, Fred Hutchinson Cancer Research Center, Seattle, Wash.Anthony Howell, MD, a professor of medical oncology, University of Manchester, Manchester, U.K.Therese Bevers, MD, medical director, Cancer Prevention Center, University of Texas M.D. Anderson Cancer Center, Houston.
© 2012 WebMD, LLC. All rights reserved.
More from WebMD