PHILADELPHIA Women who take hormones to relieve symptoms of menopause could be increasing their risk of developing ovarian cancer no matter what type of hormones, according to new research.

Researchers found women who used hormone replacement therapy for a nine-year period faced a 29 percent higher risk of developing ovarian cancer than women who never used the therapy.

Many studies on menopausal hormone therapy and cancer have shown "small increased risks" but do not examine whether the risks differ between women taking estrogen and women taking estrogen and progestin, study researcher Konstantinos Tsilidis told reporters here today (Nov. 9).

The new study found the increased risk remained regardless of the types or combinations of hormones taken, regimens, or route of administering the hormones, said Tsilidis, a postdoctoral fellow at the Cancer Epidemiology Unit at the University of Oxford.

The finding is consistent with current recommendations from the National Institutes of Health that women should take hormone therapy for no more than five years, because of cancer risks .

Tsilidis and colleagues looked at the hormone therapy use of 126,920 women who were part of the European Prospective Investigation into Cancer and Nutrition. Of those women, 45 percent had used hormone replacement therapy, including a combination of estrogen and progestin, estrogen only, or other forms of the therapy.

Over nine years, 424 of those women were diagnosed with ovarian cancer, according to the study.

Researchers found the increased risk only in women who had used the hormone therapy for longer than five years, Tsilidis said.

Previous studies have linked long-time use of hormone replacement therapy with increased cancer risks. A 2009 study of more than 909,000 healthy women in the Journal of the American Medical Association found that no matter the dose or type of hormone therapy, the risk of developing ovarian cancer was higher among current users than among women who'd never taken hormones.

And a study of 16,608 postmenopausal women, published this year in the Journal of the American Medical Association, showed that taking estrogen and progestin increased risk of developing breast cancer by 1.25 times, and increased the risk of dying from breast cancer by two times.

"The same way that it's true for breast cancer , current use and duration of use (of hormones) seem to have an effect" on ovarian cancer risk, said Dr. Judy Garber, president of the American Association for Cancer Research.

The new study was presented today at the Frontiers in Cancer Prevention Research Conference, held by the American Association for Cancer Research.