Last updated: Jan 06, 2009
Taking estrogen may increase a woman's risk of getting breast cancer.
Estrogen is probably the hardest-working hormone in a womans body, but it also has a dark side: Research has determined that estrogen often plays a key role in the development of breast cancer, especially after a woman reaches menopause. How? The estrogen in a womans body seems to raise breast cancer risk by encouraging the growth of breast tissue, which can speed up an existing tumors growth. Here's what you need to know.

Combination hormone therapy (HT): If youre considering taking estrogen and progestin (a synthetic form of the hormone progesterone) to give you relief from annoying menopause symptoms like hot flashes and night sweats, be sure to limit the time youre on the drugs. Thats because over time your breast cancer risk climbs, says JoAnn Manson, MD, professor of medicine at Harvard Medical School and author of Hot Flashes, Hormones & Your Health.

"In the Womens Health Initiative (WHI) trial, when women got seven years of estrogen alone, there was no increased risk of breast cancer, but after four to five years on combined hormone therapy, the risk emerges," she says. In fact, over time, estrogen plus progestin can raise a womans risk for breast cancer by 24%; even if you take estrogen on its own for more than 10 to 15 years, your risk may still go up.

Dr. Manson was a coauthor on a March 2008 study in the Journal of the American Medical Association that followed up on the WHI trial. It showed that even after the women stopped taking combination HT, their breast cancer risk remained elevated. "The risk of breast cancer does decline after stopping hormone therapy," she stresses, "but if a tumor has formed while a woman is on hormones its very likely to come to light even after she stops hormones, so there is some residual risk. Stopping drug therapy doesnt mean a tumor evaporates, but the risk gradually declines."

HT and early diagnosis of breast cancer: If you have no family history of the disease, youve probably been encouraged to get your first mammogram by age 40 and every one to two years after that to help ensure that any tumor is caught early, when its most treatable. Thats good advice, but taking HT may complicate things. "Estrogen-and-progestin HT can lead to increased mammographic density"—denser breast tissue—"that can obscure breast tumors and delay diagnosis," says Dr. Manson. Denser breasts are believed to be an independent risk factor for breast cancer, but they also make it harder to accurately read a mammogram and that "can lead to abnormal mammograms that may require extensive follow-up and anxiety about repeat testing and even unnecessary biopsies," Dr. Manson adds.

HT and risk for benign breast disease: In April 2008, the Journal of the National Cancer Institute found that postmenopausal women whod taken estrogen on its own doubled their risk of a noncancerous type of breast disease, but one thats associated with a higher risk of breast cancer. A September 2008 study led by the same author, Thomas E. Rohan, MD, PhD, an epidemiologist at the Albert Einstein College of Medicine, in New York City, found similarly disturbing evidence in a study of women taking estrogen and progestin: Combined HT raised a womans risk of benign breast disease by 74%.

Estrogen, testosterone, and breast cancer risk: Low sexual desire and vaginal dryness are two common—not to mention very unpleasant—hallmarks of menopause for many women. Estrogen can help ease the latter and researchers have looked at whether adding testosterone—another hormone thats crucial to libido, even in women—into the mix might help. The extent to which testosterone will perk up your love life is uncertain, but combining estrogen and testosterone may increase your breast cancer risk. A 2006 study collected data from more than 121,000 women who were part of the Nurses' Health Study and found that for the women who'd taken estrogen and testosterone, the risk of developing breast cancer went up 17% for every year they took the combo, compared to those whod never taken hormones for menopause symptoms.

What's Breast Cancer Hormone Therapy?
Side effects include hot flashes and other menopausal symptoms  Read more
The bottom line: "The recommendation for hormone therapy is for the lowest effective dose for the shortest duration, to minimize the risk of breast cancer and to minimize risk overall," sums up Dr. Manson.

Talk to your doctor about whether HT is right for you in the first place and, if it is, annually revisit the decision to stay on hormones. "If they develop hot flashes or irregular periods, women dont automatically go on hormones for their lifetimes anymore; they go on them if they have symptoms that are severe and arent controlled by other approaches," explains Kala Visvanathan, MBBS, assistant professor of epidemiology and oncology at Johns Hopkins Bloomberg School of Public Health, in Baltimore. "After a period of time you can reduce the dose and see if youre still getting symptoms. Rethink it on a yearly basis, asking your doctor, 'Should I continue on it, do I need it?'"

Dr. Manson suggests trying to limit combination HT to two to three years, and to no more than five years, if possible. If you have dense breasts (your doctor can tell whether you do), ask about ways to lower your cancer risk and make sure your annual mammogram and clinical breast exams are thorough and regular. You may also want to consider alternatives to HT and/or switch to a lower dose. Skip the supplemental testosterone too.

If youre in treatment for breast cancer
To keep breast cancer from coming back, your oncologist will want to keep the level of natural estrogen in your body at an all-time low; its unlikely hell OK either estrogen or combination HT while youre still in treatment. "Its very controversial and I would try to avoid it," Dr. Manson says. Instead, youre more likely to be put on medications that do just the opposite—deplete the estrogen you do have in order to prevent a recurrence. If youre prescribed raloxifene (Evista) or tamoxifen, these not only block estrogen receptors to stop a tumor from growing, but they can also do a lot to stave off another cancer. Aromatase inhibitors such as Arimidex and Femara—mainly used by postmenopausal women—keep your body from making the hormone in the first place, significantly lowering the chances that breast cancer will return.

The bottom line: If at all possible, pass up HT while youre still in treatment. If your symptoms are still poor after treatment, reevaluate the decision with your doctor.

If youre at increased risk of breast cancer
If your odds of getting breast cancer are higher than average—because you have a family history or because you carry a mutation of the BRCA-1 or BRCA-2 genes (which puts you at a much higher risk)—youre bound to wonder whether taking hormones to relieve menopause symptoms is worth it.

"If a woman is at very high risk for breast cancer, Ill try to avoid using HT," says Dr. Manson. "But if she doesnt respond to other treatments and shes highly symptomatic—disrupted sleep, severe hot flashes, vaginal dryness—and shes not getting adequate relief, a short course of hormones for two to three years should not really increase her risk." Talk to your doctor about whats right for you; you may be able to find nonhormonal relief before turning to drugs. Dr. Visvanathan notes that if youve had your uterus removed, your physician may suggest estrogen alone, which is associated with lower odds for breast cancer as are other alternatives to HT.

Keep in mind too that when it comes to breast cancer risk and hormones, researchers definitely dont have all the answers. An October 2008 Journal of the National Cancer Institute study of postmenopausal women whod taken hormones actually offered reassuring news, at least for BRCA-1 carriers: The researchers found that the BRCA-1 women whod taken estrogen alone or combined estrogen and progesterone actually had a decreased risk of breast cancer compared with those who hadnt had HT. Why? Thats not clear, says Steven Narod, MD, one of the studys authors and director of the familial breast cancer research unit at the Womens College Research Institute in Toronto.

The bottom line: Skip or postpone HT, if possible, or talk to your doctor about a short course of hormones while menopause symptoms are at their worst.