Women who rely on birth control pills or contraceptive devices that release hormones face a small but significant increase in the risk for breast cancer, according to a large study published in the New England Journal of Medicine.1 This study is the first to examine the risks associated with current formulations of birth control pills and devices in a large population.
The study followed nearly 1.8 million women in Denmark of childbearing age for over a decade. During that time period, 11,517 cases of breast cancer were identified. Although the study had some minor limitations because the authors could not take into account factors impacting the development of breast cancer like physical activity, breast-feeding, and alcohol consumption the following general conclusions were reached.
- The researchers reported that hormone users over all experienced a 20 percent increase in the relative risk of breast cancer compared to nonusers.
- For every 100,000 women, hormone contraceptive use causes an additional 13 breast cancer cases a year. That is, for every 100,000 women using hormonal birth control, there are 68 cases of breast cancer annually, compared with 55 cases a year among nonusers.
- Among those who used hormones for five years, an increased breast cancer risk persisted even after they discontinued use.
- Women who stayed on hormones for 10 or more years experienced a 38 percent increase in their relative risk of developing breast cancer, compared with nonusers. By contrast, there was no increased risk for breast cancer seen in women who used hormones for less than one year.
- The study found few differences in risk between the formulations; women cannot protect themselves by turning to implants or intrauterine devices that release a hormone directly into the uterus.
- The increased risk was not confined to women using oral contraceptive pills, but also was seen in women using implanted intrauterine devices, or I.U.D.’s, that contain the hormone progestin. (Not all I.U.D.’s release hormones.)
- Women who used an intrauterine device that releases only progestin had a 21 percent increase in risk, compared with nonusers.
- The research also suggests that the hormone progestin — widely used in today’s birth control methods — may be raising breast cancer risk.
- The study also found that the risk increased the longer women used contraceptives involving hormones, suggesting the relationship is causal.
Physicians and women alike had hoped that contemporary preparations in oral contraceptives would be associated with lower risks for developing breast cancer than the older generation of pills. This however does not appear to be the case. This is the first study with substantial data to show that newer preparations still increase the risk of developing breast cancer.
“Nothing is risk-free, and hormonal contraceptives are not an exception to that rule,” said Dr. Øjvind Lidegaard, the paper’s senior author. Doctors will need to take the time to discuss the pros and cons of different types of contraception with their patients. Hormonal contraceptives provide benefits to many women and remain among the most safe, effective and accessible options for birth control available.
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