In the past several years, many doctors have advanced the notion that it's safest to start hormone therapy soon after menopause, when women are most eager to find relief from hot flashes, mood swings and insomnia.
And indeed, there's good evidence that the potential benefits of hormone therapy (stronger bones, less heart disease and others) outweigh the potential risks (blood clots, stroke and more) during this period, according to a new scientific statement from the Endocrine Society.
But there's an important wrinkle: Recent research shows that women who start the most common type of hormone therapy — estrogen plus progestin — soon after menopause have a significantly higher risk of breast cancer than those who take the hormones later or not at all.
Soon after menopause: The evidence suggests that taking these hormones for five years soon after menopause (within five years after menopause is complete) will cause an additional seven out of 1,000 women to develop breast cancer, compared with women who forgo hormone treatment, according to Dr. Richard Santen, lead author of the Endocrine Society's new statement on hormone therapy.
Studies indicate that 15 out of every 1,000 women who do not take hormones in the five years following menopause will be diagnosed with breast cancer. In general, as women age, their underlying risk of breast cancer rises.
Later after menopause: By contrast, an extra four out of 1,000 women who take estrogen plus progestin for five years later after menopause (at least five to 10 years after this change of life) are likely to experience breast cancer, noted Santen, a professor of medicine at the University of Virginia Health System.
Why would the timing of hormone therapy make a difference when it comes to breast cancer?
The answer lies partly with estrogen, which "promotes the growth of almost everything," according to Dr. James Simon, a clinical professor at George Washington University.
While that growth-promoting effect may be good for a woman's skin, blood vessels and sex organs, it can be harmful if she harbors tiny, undetectable tumors in her breasts, Simon observed.
With the onset of menopause, many of these tumors would have been deprived of estrogen and expanded little, if at all. But when hormones are administered, tumors can start growing and become noticeable through mammograms or physical exams, leading to higher rates of reported breast cancer, Simon explained.
Progestin is also thought to play an important role by promoting cell proliferation and perhaps fueling the expansion of small tumors' blood supply, said Dr. Rowan Chlebowski, a medical oncologist with the Los Angeles BioMedical Research Institute at Harbor-UCLA Medical Center.
Why, then, would breast cancer risks decline for women who start hormone therapy later, after five or more years?
The theory here is that breast cancer cells deprived of estrogen for a significant time respond differently when they are again exposed to the hormone. Instead of promoting growth, after a sustained absence estrogen appears to wreak havoc on cancer cells and promote their death, Santen said.
That would help explain why women who took estrogen only in the largest randomized controlled trial of hormone therapy yet undertaken — the Women's Health Initiative study — had breast cancer rates 20 to 40 percent below what was expected. On average, women in the study had undergone menopause more than a dozen years earlier and had thus experienced a long gap of living without hormones.
The same reduction isn't seen in the estrogen plus progestin group, researchers believe, because of the impact of progestin.
When trying to evaluate the pros and cons of hormone therapy, make sure your doctor evaluates your breast cancer risk before you start taking hormones, said Simon, who also is president of Women's Health & Research Consultants in Washington, D.C. Most women exaggerate the risk of dying from breast cancer by a factor of 10, he noted.
For women age 50 to 59, the chance of being diagnosed with breast cancer is 2.38 percent, according to statistics from the National Cancer Institute.
Put another way, one out of every 42 women in this age group is likely to receive a diagnosis. Even if hormones add to this, "we're still talking about small risks overall," said Dr. Margery Gass, executive director of the North American Menopause Society.
STAY INFORMED, KEEP RE-EVALUATING YOUR OPTIONS
If your menopause symptoms aren't severe and you're worried about breast cancer risks, try lifestyle changes (turning down the heat in your bedroom at night, wearing layered clothing, cutting back on coffee), vaginal lubricants or other prescription options to ease symptoms. "If you can make it out a couple of years, your symptoms will probably get better," said Dr. Margery Gass of the North American Menopause Society.
If you decide on hormones, there's no need to worry about taking estrogen alone for about five years after menopause. "Breast cancer risk becomes significant in women who take estrogen for longer than five years," said Dr. Richard Santen, noting that risks become elevated the longer a woman is on hormone therapy.
If you start taking estrogen plus progestin soon after menopause, you're probably safe doing so for a couple of years. "After a year or two, work with your physician to see if you can stop the hormones or if you still need them," said oncologist Rowan Chlebowski.