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Contemporary Hormonal Contraception and the Risk of Breast Cancer.

It is estimated that worldwide 13% of women between the ages of 15 and 49 years use hormonal contraception. In Denmark, this percentage was 24% in 1995 and increased to 39% by 2012. Use of estrogen promotes the development of breast cancer; the role of progestin is unclear. A large number of studies have reported inconsistent findings of breast cancer risk among women who receive hormonal contraceptives. Whether contemporary hormonal contraception is associated with an increased risk of breast cancer is unknown. The authors report on a nationwide epidemiologic analysis of breast cancer risk among women of reproductive age in Denmark who were currently using available hormonal contraception. Associations were assessed 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. Women were excluded who had a history of cancer, venous thromboembolism, or treatment for infertility. Updated information about the use of hormonal contraception, breast cancer diagnoses, and potential confounders were obtained from nationwide registries. A total of 11,517 cases of breast cancer occurred among 1.8 million women followed on average for 10.9 years (a total of 19.6 million person-years). The relative risk of breast cancer among all current or recent users of any hormonal contraception Health, Inc. All rights reserved. 216 Obstetrical and Gynecological Survey as compared with women who had never used hormonal contraceptives was 1.20 (95% confidence interval [CI], 1.14–1.26). Breast cancer risk increased with the duration of use, from 1.09 (95% CI, 0.96–1.23) with less than 1 year of use to 1.38 (95% CI, 1.26–1.51) after more than 10 years of use (P = 0.002). The risk of breast cancer after discontinuation of hormonal contraceptives remained higher among women who had used hormonal contraceptives for 5 years or more compared with those who had not used hormonal contraceptives. There was little evidence of major differences in risk estimates associated with current or recent use of various oral combination (estrogen-progestin) contraceptives. Among women who currently or recently used the progestin-only intrauterine system, risk of breast cancer was also higher compared with in women who had never used hormonal contraceptives; the relative risk was 1.21 (95% CI, 1.11–1.33). The overall absolute increase in diagnosed breast cancers between women who had never used hormonal contraception and current and recent users of any type of hormonal contraception was 13 (95% CI, 10–16) per 100,000 person-years; this represents approximately 1 extra breast cancer diagnosis for every 7690 women using hormonal contraception for 1 year. The findings in this cohort study show that womenwho are current or recent users of contemporary hormonal contraception are at a higher risk of breast cancer compared with those who have never used hormonal contraceptives. The risk increases with the duration of use, and there is little evidence of major risk differences between specific combined oral contraceptives. The absolute increase in risk of additional breast cancers attributable to hormonal contraception is small. This risk should be weighed against important benefits of hormonal contraceptives such as good contraceptive efficacy and reduced risks of ovarian, endometrial, and possibly colorectal cancer.