TUESDAY, July 14 (HealthDay News) -- Women who take hormone replacement therapy or have taken it in the recent past have a higher risk of developing ovarian cancer, suggests new research.

In a large Danish study, compared to women who never took hormone replacement therapy, current users had a 38 percent increased risk of ovarian cancer and a 44 percent increased risk of epithelial ovarian cancer, which is cancer that begins on the outer lining of the ovary. The results were reported in the July 15 issue of the Journal of the American Medical Association.

The absolute risk for any one woman is still quite small, however. The researchers calculated that for every 8,300 women, hormone therapy would result in one extra case of ovarian cancer a year.

"Our study underlines previous evidence that postmenopausal hormones increase the risk of ovarian cancer," said the study's lead author, Lina Steinrud Morch of the gynecological clinic at the Rigshospitalet of Copenhagen University in Denmark. "The risk among women taking hormones was increased regardless of the duration of use, the formulation, the estrogen dose, regimen, progestin type or route of administration," she added.

And, although the absolute risk of ovarian cancer remained low, Morch noted, "ovarian cancer is the most lethal of gynecologic cancers. The five-year survival rates are 40 percent. Only a few risk factors for ovarian cancer are modifiable."

The study included all Danish women (909,946) between the ages of 50 to 79 at the start of the study. During eight years of follow-up, the researchers found 3,068 cases of ovarian cancer. Of these, 2,681 were epithelial ovarian cancers.

As soon as women stopped taking hormones, the risk of ovarian cancer decreased. Women who had just stopped taking hormones compared to those who were off for less than two years had a 22 percent increased risk of ovarian cancer compared to never-users. After two to four years off hormone therapy, the risk of ovarian cancer had dropped back down to normal.

The researchers weren't able to adjust the data to account for family history or for prior birth control use, which Morch said might result in an underestimation of the ovarian cancer risk.

The researchers didn't find any significant difference in risk based on how long women were taking hormone therapy or the type of hormone preparation they took.

However, Wyeth, maker of two conjugated estrogens -- Premarin and Prempro -- said the study didn't have enough women taking conjugated estrogens to determine actual risk for that type of hormone therapy.

"The findings in this study do not change what we already know about the benefits and risks of hormone therapy, which is based on data from multiple studies. Hormone therapy remains a good health-care choice for the appropriate woman seeking relief from moderate to severe menopausal symptoms," said a prepared statement from Wyeth.

"Biologically, the ovaries are intended to be in retirement after a certain age. If you try to restimulate them, it shouldn't be surprising that there are potential adverse consequences," said Dr. Victor Vogel, national vice president of research for the American Cancer Society.

"From an epidemiological standpoint, this is important, but for an individual woman, what's likely is that she'll never develop ovarian cancer," he said.

More information

To learn more about hormones and menopause, visit the U.S. Food and Drug Administration.

SOURCES: Lina Steinrud Morch, M.Sc., gynecological clinic, Rigshospitalet, Copenhagen University, Denmark; Victor Vogel, M.D., national vice president, research, American Cancer Society; prepared statement, Wyeth, July 13, 2009; July 15, 2009 Journal of the American Medical Association

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