The Collaborative Group on Epidemiological Studies of Ovarian Cancer includes data on 31,000 women with ovarian cancer from 58 studies worldwide. The first analyses, published in 2008, showed that use of hormonal contraceptives confers long-lasting protection against ovarian cancer; subsequent papers have reported on smoking (2012), body size (2012), and hormonal therapy for the menopause (2015).

Collaborators first met in 2005, and agreed that the first major report should be on the long term effects of oral contraceptives. Overall, oral contraceptives were found to cause a persistent reduction in ovarian cancer risk, with the protection being greater the longer the duration of use (Beral et al, 2008). Thus some 200,000 ovarian cancers have already been prevented worldwide by women’s past use of oral contraceptives. The report on smoking (2012) showed that while there is little association overall between smoking and risk of ovarian cancer, risks varied by type of tumour with some types being more common, and others less common, in smokers than in non-smokers. Also published in 2012, the Group’s report on body size showed that risk of ovarian cancer increases with increasing height; and, in women not taking hormone replacement therapy (HRT), with increasing body mass index. The recent report on menopausal hormone therapy showed that risk was increased in current users, even among those who had used it for less than five years duration. Further analyses are planned on other hormonal factors such as reproductive factors.

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