Editor's note: Since this story was first published, new information has been released on health risks associated with estrogen replacement therapy. On April 13, 2004, the National Institutes of Health released a statement citing evidence that estrogen-only therapy increases women's risk of stroke and deep vein thrombosis. Due to this evidence, the estrogen-only section of the Women's Health Initiative (WHI) study was halted prematurely in February 2004. In 2007, a new study of the WHI data examined the effects of hormone therapy by age group. This study found that the incidence of stroke risk increased 32 percent with hormone therapy across all age groups. It also revealed that even in younger women, there was an increased risk of breast cancer with estrogen and progestin therapy.

July 16, 2002 | Women who take estrogen for many years may be at increased risk for ovarian cancer, according to new findings published in the July 17, 2002 issue of the Journal of the American Medical Association.

In a study known as the Women's Health Initiative, researchers at the National Cancer Institute used patient interviews and medical records to track the history of hormone use and cancer among 44,241 women. Overall, women who took only estrogen were 60 percent more likely to develop ovarian cancer than women who didn't take any hormones. Among women who took estrogen for 20 years or more, the risk of the disease was roughly three times higher than average.

The findings are significant for women who have had hysterectomies and are taking estrogen alone without progesterone. Women who took estrogen combined with the hormone progestin -- a synthetic form of progesterone -- did not seem to be at increased risk for ovarian cancer.

The study raises the second red flag in a week for the millions of women who take hormone replacements. The NCI announced last week that on May 31 it had halted a separate study involving the combination of estrogen and progestin -- the second most prescribed drug in the nation -- years ahead of schedule after researchers noted an alarming increase in breast cancer, stroke, and heart disease among women taking the hormones. The study did not examine the affects on younger women taking birth control pills, which are still believed to be safe.

Hormone replacement therapy is often prescribed to ease the symptoms of menopause, such as hot flashes and mood swings. These symptoms are merely annoying for some women, while others find them intolerable. Until recently, hormone replacement therapy was touted not only for relieving the symptoms of menopause, but also for protecting against heart problems -- something the Women's Health Initiative study has challenged.

The WHI study of estrogen-only hormone therapy involved women who participated in a mammography screening program dating back to 1973. All women in the study were postmenopausal; their average age at the start of the study was 56. Some had had hysterectomies (surgery to remove the uterus and sometimes one or both ovaries), but all had at least one ovary.

According to the National Women's Health Information Center, the combination of estrogen and progestin is much less likely than estrogen alone to cause uterine cancer. Past studies have also strongly suggested that both estrogen and estrogen-progestin combinations can raise the risk of breast cancer.

The connection between hormones and ovarian cancer wasn't as clear. As reported in JAMA, previous studies found little association. However, most of those studies were relatively small and didn't make a distinction between estrogen and estrogen combined with progestin.

According to the American Cancer Society, ovarian cancer will be diagnosed in more than 23,000 American women in 2002. Approximately 13,900 of them will die of the disease.

According to an accompanying editorial by Kenneth L. Noller, M.D., chair of the department of obstetrics and gynecology at Tufts University in Boston, the latest study raises serious concerns about the safety of estrogen. "For a short time, estrogen replacement was viewed as the perfect solution for many health problems in postmenopausal women," he writes. "The association between estrogen use and ovarian cancer should be worrisome enough for clinicians to consider carefully whether to suggest estrogen-only HRT."

-- Chris Woolston, MS, is a health and medical writer with a master's degree in biology. He is a contributing editor at Consumer Health Interactive and was a staff writer at Hippocrates, a magazine for physicians. He has also covered science issues for Time Inc. Health, WebMD, and the Chronicle of Higher Education. His reporting on occupational health earned him an award from the Northern California Society of Professional Journalists.

References
Lacey JV et al. Long-term use of estrogen-only hormone therapy linked with increased risk of ovarian cancer. Journal of the American Medical Association. July 17, 2002. 288: 334-341.

Noller KL. Editorial: Estrogen replacement therapy and risk of ovarian cancer. Journal of the American Medical Association. July 17, 2002. 288: 368-369.

National Heart Lung and Blood Institute. Health risks outweigh benefits for combined estrogen plus progestin--Clinical trial stopped early in major study. July 9, 2002.

The National Women's Health Information Center. Hormone Replacement Therapy. August 2001.

American Cancer Society. Cancer Reference Information. How many women get ovarian cancer? 2001.

WHI Study Finds No Heart Disease Benefit, Increased Stroke Risk With Estrogen Alone. NIH News. April 13, 2004.

National Women’s Health Information Center. Hormone Therapy Doesn’t Boost Heart Attack Risk in Younger Women: Study. April 2007.