medwireNews: A Danish population-based study shows that women who are current or recent users of contemporary hormonal contraceptives have an elevated risk for developing breast cancer relative to those who have never used such measures, but the absolute increase in risk remains small.
In an editorial accompanying the study in The New England Journal of Medicine, David Hunter (University of Oxford, UK) notes that the findings are in line with previous research and show that “a risk that was initially reported with the use of older, often higher-dose formulations, also applies to contemporary formulations of oral contraceptives.”
The researchers and editorialist agree, however, that the elevated breast cancer risk needs to be balanced against the benefits of hormonal contraceptives, which include not only effective contraception but also reduced risks for ovarian, endometrial, and colorectal cancers.
The analysis included nearly 1.8 million Danish women aged 15–49 years between 1995 and 2012 who were followed-up for an average of 10.9 years, during which time 11,517 incident breast cancers were diagnosed.
Current and recent (discontinued within previous 6 months) users of hormonal contraception had a 1.20-fold higher risk for breast cancer relative to never users after adjustment for age, family history of premenopausal disease, history of polycystic ovary syndrome, and other confounding factors, reports the team led by Lina Mørch, from Rigshospitalet in Copenhagen, Denmark.
The risk rose with the duration of use, such that women who had used hormonal contraceptives for less than a year had a 1.09-fold increased risk versus never users whereas those with over 10 years of use had a 1.38-fold higher risk.
Mørch et al also found that the increased risk for breast cancer persisted for at least 5 years after discontinuation among individuals who had used such contraceptive measures for 5 years or more, but not among those who discontinued before this time. The editorialist cautions, however, that this result be regarded as preliminary as “the increase in risk would not have been significant with adjustment for multiple comparisons involving different categories of duration and time since last use.”
Although there were no major differences in risk with the use of different combined oral contraceptives, women who currently or recently used the oral or intrauterine formulation of the progestin-only contraceptive levonorgestrel were at increased risk for developing breast cancer, with corresponding relative risks of 1.21 and 1.93 compared with never users. There were few breast cancer cases among women using the progestin-only implant or depot medroxyprogesterone acetate, the team reports.
They study authors also calculated the absolute risk difference, finding an overall increase of 13 cases per 100,000 person–years among current and recent users of hormonal contraceptives, which they say equates to “approximately 1 extra breast cancer for every 7690 women using hormonal contraception for 1 year.”
In an independent comment to the press, Michael Jones (The Institute of Cancer Research, London, UK) noted: “While the findings looked at the most up-to-date hormonal contraceptives used in Denmark at the time the study began, that was still a decade or more ago. In that time, new contraceptives, using for example a lower hormone dose, have been introduced.
“It would be interesting to see what effect these have on the association between hormone-based contraception and pre-menopausal breast cancer – but we will have to wait many years for that data.”
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