New research shows women who take hormone replacement therapy (HRT) to combat the symptoms of menopause are at a higher risk of developing ovarian cancer.
The International Collaborative Group on Epidemiological Studies of Ovarian Cancer, a team of researchers organized by Oxford University, conducted a meta-analysis of 52 studies involving more than 21,000 women from North America, Europe and Australia. The team found that women aged 50 years old and above, who were taking HRT, were 40 percent more likely to develop two of the four types of ovarian cancer.
Sir Richard Peto, co-director of the Clinical Trial Service Unit at Oxford University and lead researcher, reported that for every 1,000 women who took HRT for five years, there would be one extra ovarian cancer patient.
For every 1,700 women, there would be one extra death due to either serous or endometrioid ovarian cancer, the two most common types of ovarian cancer. Higher risk levels for mucinous and clear cell ovarian cancers were not associated with HRT, according to the study.
"The definite risk of ovarian cancer even with less than five years of HRT is directly relevant to today's patterns of use -- with most women now taking HRT for only a few years -- and has implications for current efforts to revise UK and worldwide guidelines," said co-author Prof. Dame Valerie Beral.
The researchers emphasized that the risk is significant from a statistical viewpoint, but the risk of developing ovarian cancer is a relatively small one because of the relative rarity of ovarian cancer.
The American Cancer Society predicts that 21,000 women will be diagnosed with ovarian cancer this year, and 14,000 will die from the disease.
However, because ovarian cancer can be fatal, it is worth taking the results of the study into consideration in revising treatment guidelines for ovarian cancer.
The researchers are not claiming a cause-and-effect relationship between HRT and ovarian cancer. Instead, they are saying that HRT likely contributed to the ovarian cancer, although the researchers say they do not know the mechanism.
The results were the same for women who were taking estrogen only and women who were taking a combination of both estrogen and progesterone. Other factors, such as age at which HRT began, weight, use of oral contraceptives, alcohol, tobacco and hysterectomy were also ruled out.
HRT was increasingly popular in the 1990s as a way to treat menopausal symptoms such as hot flashes, vaginal dryness and loss of sex drive. However, in 2002, use of HRT plummeted when the so-called Million Women Study by the Women's Health Initiative found that women who took HRT were found to have dramatically higher risk for breast cancer, heart attack, stroke and blood clots.
Since then, debate has raged over the merits of the study, which relied on questionnaires answered by the women who participated in the study.
In 2012, a reappraisal of the study claimed the findings were irrelevant for women over 50 years old who were taking HRT to ease the symptoms of menopause.
In 2007, another study found that women who took HRT were 20 percent more likely to develop ovarian cancer than women who did not take HRT.
The results of the most recent study are detailed in The Lancet.
