Mørch, L. S., Skovlund, C. W., Hannaford, P. C., Iversen, L., Fielding, S., & Lidegaard, Ø. (2017). Contemporary Hormonal Contraception and the Risk of Breast Cancer. The New England Journal of Medicine, 377(23), 2228-2239. https://doi.org/10.1056/NEJMoa1700732
Mørch LS, Skovlund CW, Hannaford PC, Iversen L, Fielding S, Lidegaard Ø. Contemporary Hormonal Contraception and the Risk of Breast Cancer. N Engl J Med. 2017;377(23):2228-2239. doi:10.1056/NEJMoa1700732
Mørch, Lina S., et al. "Contemporary Hormonal Contraception and the Risk of Breast Cancer." The New England Journal of Medicine, vol. 377, no. 23, 2017, pp. 2228-2239.
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Danish study links hormonal contraception to higher breast cancer risk
Current or recent hormonal contraception use was linked to higher breast cancer risk. The nationwide Danish cohort tracked 1.8 million women aged 15 to 49 for about 11 years. The relative risk reached 1.38 after more than 10 years of use.
Study at a glance, nationwide prospective cohort of 1,797,932 women: Hormonal contraception use was linked to higher breast cancer risk. Source: Mørch LS et al., 2017, PMID 29211679.
Key Findings
Of 1,797,932 women followed a mean 10.9 years, 11,517 had breast cancer. Current or recent users: relative risk 1.20 (95% CI, 1.14 to 1.26) versus women who had not used hormonal contraception.
Relative risk rose with duration of current or recent use: 1.09 (95% CI, 0.96 to 1.23) under 1 year, 1.38 (95% CI, 1.26 to 1.51) beyond 10 years (P = 0.002).
After 5 or more years of use, a raised risk appeared to last at least 5 years after stopping. Past use under 5 years showed no increased risk.
Current or recent levonorgestrel-releasing intrauterine system users had a relative risk of 1.21 (95% CI, 1.11 to 1.33) versus women who had not used hormonal contraception.
Current and recent users had 13 (95% CI, 10 to 16) extra breast cancers per 100,000 person-years, about 1 extra for every 7690 women using hormonal contraception for 1 year.
Interpretation
This cohort study used Danish health records to track women of childbearing age. Women already treated for infertility were left out. The authors ran a bias check. They found it unlikely that an unmeasured factor could erase the result. The authors note their models lacked data on some risk factors, such as alcohol use and exercise. The authors say the added breast cancers among younger women are likely few, and that this risk should be weighed against the benefits of birth control. The findings support larger studies on breast cancer risk across different birth control methods and lengths of use.
RRM Context
Hormonal contraception is a suppressive medication. It overrides the ovulatory cycle. Restorative reproductive medicine looks for what causes cycle problems and pain, and works with ovulation. The Danish cohort adds long-term safety data on suppressive medications: risk rose with years of use.
Our editorial summary of this paper, not the article's abstract.
Abstract
Background
Little is known about whether contemporary hormonal contraception is associated with an increased risk of breast cancer.
Methods
We assessed associations between the use of hormonal contraception and the risk of invasive breast cancer in a nationwide prospective cohort study involving all women in Denmark between 15 and 49 years of age who had not had cancer or venous thromboembolism and who had not received treatment for infertility. Nationwide registries provided individually updated information about the use of hormonal contraception, breast-cancer diagnoses, and potential confounders.
Results
Among 1.8 million women who were followed on average for 10.9 years (a total of 19.6 million person-years), 11,517 cases of breast cancer occurred. As compared with women who had never used hormonal contraception, the relative risk of breast cancer among all current and recent users of hormonal contraception was 1.20 (95% confidence interval [CI], 1.14 to 1.26). This risk increased from 1.09 (95% CI, 0.96 to 1.23) with less than 1 year of use to 1.38 (95% CI, 1.26 to 1.51) with more than 10 years of use (P=0.002). After discontinuation of hormonal contraception, the risk of breast cancer was still higher among the women who had used hormonal contraceptives for 5 years or more than among women who had not used hormonal contraceptives. Risk estimates associated with current or recent use of various oral combination (estrogen-progestin) contraceptives varied between 1.0 and 1.6. Women who currently or recently used the progestin-only intrauterine system also had a higher risk of breast cancer than women who had never used hormonal contraceptives (relative risk, 1.21; 95% CI, 1.11 to 1.33). The overall absolute increase in breast cancers diagnosed among current and recent users of any hormonal contraceptive was 13 (95% CI, 10 to 16) per 100,000 person-years, or approximately 1 extra breast cancer for every 7690 women using hormonal contraception for 1 year.
Conclusions
The risk of breast cancer was higher among women who currently or recently used contemporary hormonal contraceptives than among women who had never used hormonal contraceptives, and this risk increased with longer durations of use; however, absolute increases in risk were small. (Funded by the Novo Nordisk Foundation.).
