The findings expand upon the landmark Women's Health Initiative study of 2002, which found that a common estrogen-plus-progestin treatment increased a woman's risk for heart attacks, breast cancer and strokes.

"In our study, we found the same increased risk of breast cancer, but we didn't find an increased risk of heart disease," said Dr. Irene Su, an assistant professor of reproductive medicine at the University of California, San Diego, and the study's lead author.

The research suggests that the WHI findings on hormone therapy -- derived largely from Caucasian women -- may not apply across all racial and ethnic groups.

"Those risks and benefits may not be the same in Asian women as in white women," Su told Reuters Health. "You really can't assume it is going to be the same."

Some women take hormone pills containing estrogen and progestin or estrogen alone -- marketed as Prempro or Premarin, respectively -- to treat hot flashes and other symptoms of menopause.

The therapy was also used in the U.S. to prevent postmenopausal women from developing heart disease, osteoporosis and other chronic illnesses -- until the WHI results curbed its use for these purposes.

Caution about the treatment continues to grow.

In April, researchers from Boston's Dana-Farber Cancer Institute presented a study at the American Association for Cancer Research meeting in Chicago that found any type of hormone therapy -- including estrogen alone -- may raise a woman's breast cancer risk if she takes it for more than 10 years. And the risk continues to increase the longer women take the drugs, the findings suggested.

For the new study, researchers tracked records from about 16,000 postmenopausal women of Chinese descent covered by Taiwan's national health insurance system starting in 1997 -- before the risks of hormone therapy were well known.

Of these women, close to 6,000 received either combination therapy for seven months, on average, or estrogen-only therapy for nine months. The researchers compared their health outcomes with those of another 10,000 women who did not get hormone treatment.

Su's team found that over an average of nine years, there was no difference in heart attacks or heart-related deaths based on treatment.

Women who used estrogen- and progestin-containing drugs suffered a heart attack or cardiac death at a rate of seven per 10,000 participants each year, compared to a rate of 10 per 10,000 participants annually among those who didn't receive the pills.

The difference in rates between the groups -- three per 10,000 -- was not statistically significant, meaning it could have occurred by chance, the researchers reported in Menopause.

Taking estrogen-only drugs also didn't seem to affect a woman's risk of heart disease.

Su's team found, however, that the combination pill was linked to a higher rate of breast cancer. The increased risk tied to estrogen-progestin drugs was 12 additional breast cancer cases for every 10,000 women over one year. Overall, there was a 50 percent increase in the rate of breast cancer with the use of combined therapy.

The researchers found little difference in rates of breast cancer and stroke in women who took or didn't take estrogen-only pills -- in contrast to the WHI study which found less breast cancer and more strokes in the women who used estrogen alone over non-hormone users.

Su and her colleagues modeled their study design after the WHI, choosing a similar time frame, criteria for being included in the trial and therapy regimen. Their study was funded by the American Society of Reproductive Medicine.

Amy Allina, program director at the National Women's Health Network, an advocacy group, described the findings as useful but cautioned against assuming that they hold true for Chinese-American women.

"There are important changes we see in immigrant populations with respect to diet, physical activity and body size," which could affect risks related to hormone therapy, said Allina, who wasn't involved in the study.

The long-term use of hormone therapy to treat heart disease or osteoporosis is no longer advised, but it is "the only well-proven treatment for hot flashes," she told Reuters Health.

"Some women might be willing to take on some increased risk of breast cancer to get that relief," she added.

SOURCE: bit.ly/ISTKRe Menopause, online March 26, 2012.

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