Hormone replacement therapy may be associated with increased risk of ovarian cancer

A meta-analysis study, led by researchers from the University of Oxford (UK), has indicated that short-term use of hormone replacement therapy (HRT) may be associated with an increased risk of developing the two most common types of ovarian cancer. The results of the study were published recently in The Lancet.

The study investigated 52 epidemiological studies that included in total 21,488 women diagnosed with ovarian cancer, mainly originating from North America, Europe and Australia. The findings indicate that women who take HRT for a few years have an estimated 40% increased risk of developing ovarian cancer compared with women who have never taken HRT.

“For women who take HRT for five years from around age 50, there will be about one extra ovarian cancer for every 1000 users and one extra ovarian cancer death for every 1700 users,” explained Sir Richard Peto from the University of Oxford.

Currently in the UK and USA approximately 6 million women are taking HRT. Established WHO, US and European HRT guidelines do not mention the associated risk of ovarian cancer, and UK guidelines state that ovarian cancer risk may be increased with long-term use. Previous studies have been too small to assess the risks from just a few years of HRT use.

In this analysis, the international Collaborative Group on Epidemiological Studies of Ovarian Cancer researchers found that there was a significantly higher risk of developing ovarian cancer in current users or women who had taken HRT within the last 5 years. However, although the risk of ovarian cancer decreased over time after stopping treatment, women who had utilized HRT for a minimum of 5 years still had an increased risk of ovarian cancer 10 years later.

The effect of HRT on the risk of developing ovarian cancer was the same for the two most common types of HRT (estrogen only or estrogen together with progestagen). Similarly, the proportional increase in risk was not significantly affected by the age at which HRT was begun, body size, previous use of oral contraceptives, hysterectomy, alcohol use, tobacco use, or family history of breast or ovarian cancer.

Co-author Dame Valerie Beral from the University of Oxford explained: “The definite risk of ovarian cancer even with less than 5 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.”

Sources: Collaborative Group on Epidemiological Studies of Ovarian Cancer. Menopausal hormone use and ovarian cancer risk: individual participant meta-analysis of 52 epidemiological studies. The Lancet, DOI: 10.1016/S0140-6736(14)61687-1 (2015); University of Oxford press release