(Reaffirmed September 2022)
On December 7, 2017, a cohort study analyzing the risk of invasive breast cancer in women who used hormonal contraception was published in the New England Journal of Medicine 1. The study was designed to assess the influence of hormonal contraceptive use on the development of cardiovascular disease and cancer in a national cohort of Danish women. The authors found that compared with women who never used hormonal contraception, the overall relative risk of invasive breast cancer among women who were current or recent users of any hormonal contraception was 1.20 (95% confidence interval [CI], 1.14–1.26). Relative risk increased with duration of use, ranging from 1.09 (95% CI, 0.96–1.23) for less than 1 year of use to 1.38 (95% CI, 1.26–1.51) for use longer than 10 years. In general, risk was similar among different formulations or preparations of combined oral contraceptives. The results among progestin-only methods were inconsistent, with no statistically significant increased risk with some progestin-only methods but an increased risk with others, including oral levonorgestrel (which is not marketed for contraception in the United States). Among women who used the levonorgestrel-releasing intrauterine device (LNG-IUD), the relative risk of breast cancer was 1.21 (95% CI, 1.11–1.33) compared with never-users of hormonal contraception, but the risk did not increase with duration of use.
- This study found that the overall risk of breast cancer among hormonal contraceptive users is low. Because of the low baseline risks in the age groups using hormonal contraception (ie, premenopausal women), the risk difference between hormonal contraception users and nonusers is small. The relationship between oral contraceptive use and breast cancer has been the subject of a number of studies. Meta-analyses of these studies have shown a slight increased risk, ranging from 8–24% 2 3 4 , which is similar to the risk observed in the current study. The increased relative risk observed in the current study translates into 1 additional case of invasive breast cancer for every 7,690 women using hormonal contraception 1. This risk varied with age: for women younger than 35 years, there was 1 additional case of invasive breast cancer for every 50,000 women using hormonal contraception 1.
- The relationship between progestin-only contraceptives and breast cancer risk warrants further study. The risks for different progestin-only formulations were inconsistent and dose-response and duration-response relationships were not present, making it very difficult to interpret these findings. In this study, the LNG-IUD had a relative risk of breast cancer similar to that of combined hormonal oral contraception, whereas contraceptive implants and injectables had no observed increased risk. Methods with higher systemic levels of progestin, particularly injectables, did not seem to be associated with increased risk. The LNG-IUD had increased risk, but this risk was unchanged with duration of use.
- Hormonal contraception has other significant health benefits. The small increased risk of breast cancer identified in this study needs to be interpreted in the context of the benefits of hormonal contraceptive use. The noncontraceptive benefits of hormonal contraception are well-established and include decreased risk of ovarian, endometrial, and colon cancer 4. Because of protection against these cancers, overall cancer risk may be slightly lower in hormonal contraceptive users compared with nonusers, even with the small increased breast cancer risk observed in this study 5. The benefits of hormonal contraceptives in preventing pregnancy are also important. In 2015, the maternal mortality rate in the United States was 26.4 deaths per 100,000 women 6, which is double the risk of developing invasive breast cancer (13 additional breast cancers per 100,000 users) found among women in the current study who used hormonal contraception 1.
- The study had several limitations. This study did not account for some important potential confounders, including breastfeeding, alcohol consumption, and physical activity, and was restricted to a northern European population, potentially limiting the ability to generalize these results to other populations.
Patient Counseling and Shared Decision Making
This study underscores the importance of shared decision making in counseling women about contraception. Shared decision making requires providing women with current and accurate information regarding the efficacy, noncontraceptive benefits, and risks associated with hormonal and nonhormonal contraceptives. This information should be provided in a clear, balanced, and supportive way to enable each woman to understand the expected outcomes associated with her various options and empower her to make an informed decision consistent with her values and preferences. Patients who are considering hormonal contraception can be counseled that:
- This recent study showed that women who use hormonal birth control methods may have a small increased risk of breast cancer, but the overall risk of breast cancer in hormonal birth control users remains very low.
- Hormonal birth control is very effective in preventing pregnancy and may lower a women’s overall risk of cancer by providing protection against other types of cancer.
- There are nonhormonal methods of birth control that are also good options.
- Women can do things to help lower their risk of breast cancer, like breastfeeding, getting more exercise, and limiting alcohol intake.
For more information on contraceptive options, visit https://www.acog.org/Womens-Health/Birth-Control-Contraception.