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Menopause Health Center

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Menopause Hormone Therapy: 'Safe' Time?

New Studies Probe Timing of Hormone Replacement Therapy and Breast Cancer Risk

New Findings on Hormone Replacement Therapy

The two new studies agree on four things:

1. The long-term breast cancer risk from estrogen-plus-progestin therapy is real. Rowan Chlebowski, MD, PhD, who worked on The New England Journal of Medicine study, says that risk has been characterized as being "small," but at least 20,000 cases of breast cancer per year in the U.S. may be due to hormone therapy. "It's not a hypothetical number, something that never happens," Chlebowski tells WebMD.

2. Quitting hormone therapy cuts breast cancer risk. The increased breast cancer risk from hormone replacement therapy appears to end about two years after quitting hormone therapy. That's "good news," Chlebowski tells WebMD. In the WHI data, "it looked like the risk starts to go down right away. And after between one and two years, it looks like pretty much like that risk is gone," says Chlebowski, who works at the Los Angeles Biomedical Research Institute at the Harbor-UCL Medical Center.

Eugenia Calle, PhD, who worked on the study published in Cancer, agrees. "For women who've stopped using estrogen plus progestin, our data suggest that their risk for breast cancer will go back down in a fairly short period of time," says Calle, who recently retired as the American Cancer Society's vice president of epidemiology.

3. Mammography rates don't explain the drop in breast cancer after quitting hormone replacement therapy. Using WHI data, Chlebowski's team confirmed that breast cancer rates really did drop after women quit hormone replacement therapy; it wasn't because of a change in mammography use.

4. Breast cancer risk is greater with estrogen-plus-progestin than estrogen alone. "We do not have evidence from the WHI clinical trial that estrogen increases breast cancer. It's the combination of estrogen and progestin" that's the issue, Marcia Stefanick, PhD, tells WebMD. Stefanick works at the Stanford Prevention Research Center and was one of Chlebowski's colleagues in reviewing the WHI data.

Calle puts it this way: "Estrogen plus progestin is considerably worse in terms of breast cancer risk than estrogen alone, and we've known that for some time."

Just taking estrogen probably isn't a solution for women who still have their uterus, because doing so would raise their risk of uterine and endometrial cancer. Women who've had a hysterectomy don't have to worry about that.

"We had a huge increase in endometrial cancer back in the '70s that was reported when women were taking just estrogen if they had a uterus. So I don't think very many people would want to go back to unopposed estrogen [estrogen without progestin] as the approach," says Stefanick.

But the studies have their differences, too.

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