Women may be asking about birth control pills and the risk of breast cancer after publication of a highly publicized study. Researchers from Denmark reviewed the records of 1.8 million women over about 11 years (19.6 million person-years), during which 11,517 cases of breast cancer occurred. Compared to women who had never used hormonal contraception, the relative risk (RR) of breast cancer among all current and recent users of hormonal contraception was 1.20 (95% confidence interval [CI], 1.14-1.26). The risk increased with duration of usage from a RR of 1.09 with less than one year of hormonal contraceptive use to 1.38 with > 10 years of usage. The risk remained higher after discontinuation if contraception was used for > 5 years. Interestingly, the intrauterine progestin-only system also was associated with a higher risk of breast cancer (RR, 1.21; 95% CI, 1.11-1.33). The increase in breast cancer risk associated with hormonal contraception calculates to about one extra breast cancer for every 7,690 women using hormonal contraception for one year. The authors concluded that while the risk is small, there was a higher risk of breast cancer among women who currently or recently used contemporary hormonal contraceptives than among women who had never used hormonal contraceptives. Also, this risk increased with longer use (N Engl J Med 2017; 377:2228-2239).
The authors of an accompanying editorial noted that the 20% higher risk of breast cancer associated with hormonal contraceptives found in this study is about the same observed in other large studies. The difference is that the new study used more modern formulations of oral contraceptives. But the low risk of breast cancer must be combined with the low incidence of cancer in younger women, along with the protective effects of oral contraceptives against other cancers, including ovarian, endometrial, and colorectal cancers, later in life. Still, the search for a hormonal contraceptive that does not raise the risk of breast cancer must continue (N Engl J Med 2017;377:2276-2277).