Oral Contraception Provides Long Term Protection Against Ovarian Cancer

Oral contraception confers long term protection against ovarian cancer, concludes a study published in The Lancet. Taking the Pill for 15 years halves the risk of ovarian cancer, the study by the Collaborative Group on Epidemiological Studies of Ovarian Cancer found, with a significant reduction in risk still occurring 30 years after pill use has ceased. Scientists have known for a long time that oral contraceptive use is linked to a reduced incidence of ovarian cancer, but were unclear of exactly how long protection continued after women stopped taking the pill.

Valerie Beral, from Cancer Research UK's Epidemiology Unit, Oxford, and a large number of collaborators, undertook a meta-analysis of 45 epidemiological studies involving the use of oral contraceptives and the subsequent risk of ovarian cancer. Of the 45 studies, undertaken in 21 countries, 13 were cohort studies following women prospectively (over time) and 32 were case-controlled studies of women who had already developed ovarian cancer, comparing them to a control group of women who had not, with both groups providing details about whether they had taken the pill in the past (retrospectively).

Overall data was available for 23,257 women diagnosed with ovarian cancer between 1973 and 2001, and for 87 303 women without ovarian cancer. Additionally, for each individual woman in the meta-analysis the original investigators were approached to provide data on ethnic group, education, age at first birth, family history of breast cancer, age at menarche, menopausal status, use of horm! one replacement therapy, height, weight, body-mass index, alcohol use and smoking. Such confounding actors were examined by comparing results before and after stratification for each variable. The results showed:


- Overall, 31% (7308) of women with ovarian cancer and 37% (32 717) of controls without ovarian cancer had used oral contraceptives, with an average duration of use of 4???4 and 5???0 years, respectively;



- The longer women used oral contraceptives, the lower their risk of developing ovarian cancer. For each additional five years of use, women reduced their risk by a further 20%;



- The protective effects of oral contraception continued well beyond ceasing use, but declined with time. Current users and those who had stopped taking contraceptives less than 10 years previously reduced their risk by 29 %, those who stopped in the previous 10 to 19 years by 19 % and those who stopped 20 to 29 years earlier by 15 %.


- Oral contraceptive use in the 1960s, 1970s and 1980s was associated with similar reductions in ovarian cancer risk, despite oestrogen doses halving over this period.


Over the course of the last 50 years, write the authors, around 200 000 incident cases of ovarian cancer and 100 000 deaths have already been prevented by oral contraceptive use. Furthermore, they add, "the number of cancers prevented each year is likely to increase substantially in the future, with the further ageing of past users of oral contraceptives and the increasing numbers of new users, especially in middle-income and low-income countries".
















Reviewing the limitations of their study, the authors caution that there is a possibility that some studies might have been missed in the meta analysis. In addition, other studies are still collecting data, and therefore could not contribute to the analysis. However, these studies would have increased the number of cases by only 3 %, and are therefore unlikely to have affected the overall result. A further limitation of observational studies, they write, is that they can not identify exactly how the Pill caused the observed reduction. The benefits, however, are likely to have resulted from the suppression of ovulation.


In an accompanying commentary Eduardo Franco ( McGill University, Montreal, Canada) and Eliane Duarte-Franco (Institut National de Sant?© Publique, Montreal, Canada) write: "As for the link between oral contraceptives and ovarian cancer, today's collaborative analysis brings unequivocal good news. Women and their health-care providers are once again at a balancing act of judging risks versus benefits."


Ovarian cancer and oral contraceptives: collaborative reanalysis of data from 45 epidemiological studies including 23,257 women with ovarian cancer and 87,303 controls.

Collaborative Group on Epidemiological Studies of Ovarian Cancer.

The Lancet (2008:371:303-14).


Cancer Research Summaries are overviews of important cancer research findings that have been reported in leading cancer publications. The Cancer Research Summaries are provided by the Cancer Media Service (CMS) in collaboration with Nature Clinical Practice Oncology .



This summary is provided by the Cancer Media Service which is operated by The European School of Oncology.


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