Women who take hormone replacement therapy to ease the symptoms of menopause have a significantly increased risk of ovarian cancer, a study of more than 21,000 women has found.
In a discovery likely to change treatment guidelines for millions of women globally, the analysis of 52 epidemiological studies concluded that women who use HRT, even for just a few years, are 40 per cent more likely to develop ovarian cancer than women who have never used the treatment.
The research published in The Lancet shows that among women aged from about 50 who take HRT for five years, there will be one extra ovarian cancer for every 1000 users and one extra ovarian cancer death for every 1700 users.
While doctors have long suspected HRT may cause some ovarian cancers, this is the largest ever study to assess the link and quantify the risk. It mainly included studies of women from Australia, North America and Europe.
The researchers from the International Collaborative Group on Epidemiological Studies of Ovarian Cancer said the increased risk related to the two most common forms of ovarian cancer (serous and endometrioid) and applied to women taking the two main types of HRT (preparations containing oestrogen only or oestrogen together with progestogen).
Furthermore, they said the increased risk was not altered by the age at which HRT began, body size, past use of oral contraceptives (which are known to protect against ovarian cancer), hysterectomy, alcohol use, tobacco use, or family history of breast and ovarian cancer.
Australian experts welcomed the study as more useful information about the risks of HRT, but said women should not panic about it because ovarian cancer remains rare, with about 1500 diagnoses each year.
Professor of Obstetrics and Gynaecology at the University of Melbourne and Royal Women’s Hospital Martha Hickey described the research as the best information to date on the link between HRT and ovarian cancer. She said although the risk was small, it was worth considering because ovarian cancer can be fatal.
“The chances of it happening are small, but on the other hand ovarian cancer has a very poor prognosis … so it’s important for that reason,” she said.
Professor Susan Davis, a leading endocrinologist at Monash University, described the risk of ovarian cancer as a “small blip” that should be weighed against the benefits of taking HRT, which remains the best available treatment for troubling menopausal symptoms such as hot flushes and sweats. Furthermore, she said HRT was associated with a lower risk of colon cancer, heart disease and improved bone density which protects against osteoporosis and fractures.
The Lancet‘s study on ovarian cancer follows great controversy about the risks of HRT over the past 13 years. In 2002, the Women’s Health Initiative study said the treatment dramatically increased the risk of heart disease, strokes, breast cancer and blood clots.
But a reappraisal of the study published in 2012 said the findings were irrelevant for women in their 50s and that the benefits of taking HRT significantly outweighed the risks for many women experiencing menopausal problems.
About 2 million Australian women are going through or approaching menopause, when menstruation ends and the body’s production of the sex hormones oestrogen and progesterone drops off. About 80 per cent experience moderate or severe symptoms.
Professor Davis said about 10 per cent of women aged 40 to 65 are using some form of HRT in Australia.