Treatment for Menopause Linked to Ovarian Cancer

Taking hormone replacement therapy (HRT) for the menopause, even for just a few years, is associated with a significantly increased risk of developing the two most common types of ovarian cancer, a group led by Oxford Univ. researchers have found.

The detailed meta-analysis of evidence looked at 52 epidemiological studies, involving a total of 21,488 women with ovarian cancer mainly from North America, Europe and Australia. The results, published in The Lancet, indicate that women who use HRT for just a few years are about 40 percent more likely to develop ovarian cancer than 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 1,000 users and one extra ovarian cancer death for every 1,700 users,” Coauthor Prof. Sir Richard Peto, who codirects the Clinical Trial Service Unit at Oxford Univ. said.

Although HRT use fell rapidly about a decade ago, this decrease has now levelled off: around six million women are still taking HRT in the UK and U.S. alone. Existing World Health Organization, U.S. and European HRT guidelines do not mention ovarian cancer, and UK guidelines, which are currently being revised, state only that ovarian cancer might be increased with long-term use. Previous studies had been too small to assess reliably the risks from just a few years of HRT use.

“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,” coauthor Prof. Dame Valerie Beral from Oxford's Cancer Epidemiology Unit, said.

The international study by the international Collaborative Group on Epidemiological Studies of Ovarian Cancer was organized by Oxford Univ. involved over 100 researchers from across the world. They analyzed individual participant data from 52 studies, comprising virtually all of the epidemiological evidence ever collected on HRT use and ovarian cancer.

They found a significantly increased risk of developing ovarian cancer in current or recent users (women who had used HRT within the past five years), but although the risk of ovarian cancer fell over time after stopping treatment, women who had used HRT for at least five years still had a somewhat 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 main types of HRT (preparations containing estrogen only, or estrogen together with a progestogen). The proportional increase in risk was not significantly affected by factors including the age at which HRT began, body size, past use of oral contraceptives, hysterectomy, alcohol use, tobacco use or family history of breast or ovarian cancer.

There are four main types of ovarian cancer, and the increase in risk was associated only for the two most common types (serous and endometrioid ovarian cancers), and not for the two less common types (mucinous and clear cell ovarian cancers).