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Insights from outside BJOG

There is an increased risk of breast cancer with hormonal contraceptive use according to research carried out 2 or 3 decades ago. Studies found a small relative risk of 1.20 for current hormonal contraceptive users – mainly oral contraceptives – compared with never users. Since then, hormone sophistication and modes of delivery have advanced, as have data collection methods, so a report from Denmark with up-to-date information is helpful (Mørch et al.NEJM 2017;377:2228–39). ‘Big data’ are available since the Danish can link national prescription fulfilment to breast cancer diagnoses and integrate personal information to take into account many previously confounding variables. They monitored all the women of their country of reproductive age and were able to calculate the risk of breast cancer developing in relation to hormone use of current contraceptive products. After following nearly 2 million women for 10 years they found a relative risk of breast cancer of 1.20 (CI: 0.96–1.23) for women using hormonal contraception compared with never users. This risk increased with duration of use and remained elevated for 5 years post cessation although this lingering risk depended on how long the contraceptive was used. Types of oral contraceptives varied within a narrow range and the increase for progestin-only intrauterine devices was similar (RR 1.21 CI: 1.11–1.33). These relative risks translate into small absolute risks being an increase of 13 per 100 000 person-years or 1 extra breast cancer case for 7 800 women using hormonal contraception for 1 year. The interpretation of these outcomes are put into perspective in an editorial by Hunter (NEJM 2017;377:2276–7) as follows: Firstly, there is a high probability of these findings being accurate given the completeness and volume of the data, the prospective collection and its consistency. Secondly, the data included women aged between 40 and 50 years when the risk of breast cancer rises, when in fact for women under the age of 35 years the absolute increased risk is only 2 per 100 000 women years. Most of the diagnoses of breast cancer in the study were in women over the age of 40 years. Thirdly, hormonal contraceptives have a wide range of advantages which need to be weighed against the small increase in breast cancer risk. These are effective contraception, decreased dysmenorrhoea, menorrhagia, anaemia, acne and other malignancies in later life such as substantial reductions in the risk of ovarian, endometrial and colo-rectal cancers. The probability is that there is a net decrease in overall cancer risk associated with using hormonal contraceptives for 5 years.