July 14 (Bloomberg) -- Women who had hormone therapy for menopause symptoms were more likely to develop ovarian cancer, regardless of the length, formulation or type of treatment they received, a Danish study found.

Women who were under treatment at the time of the study had a 38 percent higher risk of ovarian cancer than those who had never used such therapies, according to research published today in the Journal of the American Medical Association.

About 21,550 new cases of ovarian cancer, the most fatal cancer of the female reproductive system, will be diagnosed in the U.S. this year, according to the American Cancer Society. The Danish findings corroborate an April 2007 U.K. research project called the Million Women Study. The studies may make women more carefully weigh the benefits and risks of hormone therapy, which has been linked to an increased risk of breast cancer, heart attacks and stroke, according to Rowan Chlebowski, an oncologist at the Los Angeles Biomedical Research Institute.

“More negative information raises the threshold for how severe symptoms for a woman has to be,” said Chlebowski, who was not involved in the Danish research. Women whose symptoms are acute should try taking these medicines on a short-term basis and then evaluate whether they’re still needed, he said.

The study’s lead author, Lina Steinrud Morch, said in an e- mail, that the risk for ovarian cancer rises “even at durations of zero to four years.”

“The study suggests that no type of hormone seems safe regarding the risk of ovarian cancer,” Morch said. “If a woman has a special predisposition for ovarian cancer, she should consider not taking hormones.”

Research Methodology

The researchers at Copenhagen University in Denmark analyzed data on 909,946 Danish women, ages 50 to 79, from 1996 through 2005 from its national health registers. By the end of the study period, 63 percent of the women had not taken hormone therapy, 22 percent had received treatment in the past and 9 percent were current users. Among the current users, 46 percent had been in treatment for more than seven years.

During the study, 3,068 ovarian cancers were detected. Of those, 2,681 were epithelial tumors, the most common type of ovarian tumors occurring on the outer surface of the ovaries.

Two years after stopping hormone therapy, the risk of ovarian cancer is similar to the risk among those who never used the treatments, said Morch, a Ph.D. student at Copenhagen University.

Epithelial Ovarian Cancer

Among those who had epithelial ovarian cancer, current hormone therapy users had a 44 percent higher risk of developing the disease compared with those who never had the treatment, the study showed. Previous hormone therapy users had a 15 percent greater risk of the cancer versus non-users.

The researchers found that using hormone therapy results in about one extra case of ovarian cancer for roughly every 8,300 women taking the treatments each year.

“Ovarian cancer is still a rare disease,” Morch said. “So despite a 40 percent increased risk of ovarian cancer among current users of hormones, each woman will still have a very low absolute risk of developing cancer due to her hormone use. We think that hormones may still have a therapeutic place in women with severe perimenopausal symptoms and among women going into premature menopause.”

Morch said researchers aren’t sure how hormone therapy increases the risk of ovarian cancer.

Wyeth Responds

Corrado Altomare, senior director of Global Medical Affairs at Madison, New Jersey-based Wyeth, which makes the hormone replacement therapies Premarin and Prempro, said the products’ labels already mention an increased risk for ovarian cancer. The medicines are prescribed to treat moderate-to-severe hot flashes and vaginal dryness after menopause.

“The results of the paper are quite consistent with previous studies, which have observed a slight increased risk of ovarian cancer with hormone use,” he said today in a telephone interview. “Any woman who is interested in hormone therapy should be speaking to their physician about this.”

Doctors don’t know what causes ovarian cancer. Risk factors include age, weight, fertility-drug use and family history of the disease. The disease accounts for about 3 percent of all cancers in women and results in about 14,600 deaths a year in the U.S., according to the American Cancer Society.

To contact the reporter on this story: Nicole Ostrow in New York at nostrow1@bloomberg.net.

Last Updated: July 14, 2009 16:23 EDT