According to the results of a large U.S. study, older women who used hormone therapy to ease the symptoms of menopause and then discontinued it remain at increased risk of cancer. Researchers voiced surprise at the finding because their study also showed that other negative health effects disappear once women stop hormone therapy. VOA's Jessica Berman reports.

The findings are the outgrowth of a large study on hormone replacement therapy, or HRT, in menopausal and post-menopausal women called the Women's Health Initiative, sponsored by the U.S. National Institutes of Health.

The Initiative was launched in 1991 to see whether supplemental female hormones would reduce hot flashes and other symptoms of menopause in 16,600 aging women while at the same time protecting them against heart disease and osteoporosis, which causes brittle bones.

But the study was abruptly halted in 2002 when the data showed that a combination of the hormones, estrogen and progestin, in menopausal and post-menopausal women increased their risk of breast cancer.

Further analysis also showed women on HRT were at greater risk for heart disease and stroke.

Investigators then followed up with almost 1,600 women from 2002 until 2005. Those results are published in the current issue of the Journal of the American Medical Association.

Rowan Chlebowski is a medical oncologist at the Los Angeles Biomedical Research Institute and one of the study's principle investigators.

Chlebowski says it appears the risk of heart disease returns to normal after a woman stops taking the hormones, and that is good news.

"But the cancer increase was unexpected," said Chlebowski. "It raises just a new concern about [the] estrogen plus progestin kind of use."

At the time the trial was stopped, women on HRT had a 25 percent increased risk of breast cancer compared to women who were not on hormone therapy.

In their 2.5-year follow-up, the investigators reported the 25 percent risk of breast cancer persisted and, with the exception of colon cancer, there was a slightly increased risk of other cancers, including lung cancer.

Robert Wallace is a professor of epidemiology at the University of Iowa and one of the researchers who tracked study participants from 2002 through 2005.

Wallace says the large, carefully controlled hormone study leaves little doubt that HRT increases the risk of cancer.

"This is a randomized trial," he said. "It's an experiment, and that gives us a fair degree of certainty that this was related to the drug."

But Chlebowski says younger women entering menopause should not become alarmed by the findings. He says short-term use of hormone replacement therapy is not likely to be harmful.

"What we're saying here now is that taking a short term [treatment] for symptoms, which many women have, seems still like a very good idea, said Chlebowski. "But I think the concept that we can reduce disease by taking a pill and predicting what's going to happen ten years later sounds like it's a very difficult process."

The study's authors recommend that women who received hormone replacement therapy with estrogen and progestin for 3.5 to 8.5 years undergo regular cancer screenings.