Hormonal Contraception and Risk for Breast Cancer: Many Caveats

JoAnn E. Manson, MD, DrPH


December 13, 2017

Hello. I am Dr JoAnn Manson, professor of medicine at Harvard Medical School and Brigham and Women's Hospital in Boston, Massachusetts. I would like to talk with you about a recent report in the New England Journal of Medicine on hormonal contraception and risk for breast cancer.[1]

This is an observational study from Denmark that addresses the relationship between the newer, lower-dose, more contemporary formulations of hormonal contraception, including progestin-only contraceptives, and the risk for breast cancer. The study identifies a small increase in risk—about a 20% magnitude increase—and, with longer duration of treatment (10 or more years), about a 38% increase in risk.

This research is an important contribution to the literature, but the findings need to be considered with some caveats, including a few methodologic limitations and the very low absolute risks for breast cancer that were identified. In addition, we need to pay some attention to the counterbalancing benefits of hormonal contraception, which received little attention in the report.

The major strength is that this is a very large-scale study, comprising 1.8 million women who are followed through nationwide Danish registries that are linked and include information about prescription medications, breast cancer diagnoses, and some clinical characteristics of the women. The study does have some limitations, however. Although the investigators provide information on clinical characteristics such as age, education, parity, and some information on family history of cancer, they do not include information on some potentially important confounders such as age at menarche, alcohol consumption, and, most important, breast cancer screening behaviors, such as clinical breast exams and mammography. Surveillance for breast cancer may differ among women who are clearly in the medical system and receiving prescription hormonal medication and women who are not receiving these medications.

We must also consider the very small absolute risk for breast cancer in this population. These are women below the age of 50 years. In this population, there were about 1.3 extra cases of breast cancer per 10,000 women per year who used hormonal contraception. This amounts to about 1 extra case of breast cancer annually per 7700 users of hormonal contraception.

Also important to consider are some of the counterbalancing benefits. Hormonal contraception has been linked to a reduced risk for some other cancers. For example, for ovarian cancer and endometrial cancer, meta-analyses suggest about a one-third reduction in risk and some studies show a reduction in colorectal cancer as well.[2] Overall, the meta-analyses do not suggest an increase in total cancer or total mortality in women who take hormonal contraceptives.

Moreover, hormonal contraception is a very effective form of contraception that empowers women to take control of their reproduction. We also should take into account that pregnancy and childbirth themselves are not free of risk. For example, during pregnancy there is increased risk for thrombosis, particularly pulmonary embolism, and maternal mortality rates are appreciable. In developed countries, mortality rates average about 2 to 3 per 10,000 live births, and in low-income countries, rates are about 10 times higher.[3]

Will this study change clinical practice? It is important for women to have this information and it may be important for shared decision-making, with women reviewing their options for contraceptives with their healthcare providers. But it is not likely to lead to major changes in clinical practice because of these very low absolute risks and the complex benefit-risk ratio. For older women, women who are in their 40s, taking contraception causes a higher baseline risk for breast cancer than that of younger women (in their 20s and 30s). Older women may also have a slightly higher risk for cardiovascular complications with these contraceptives.

Of course, a decision about taking hormonal contraceptives needs to be made only after a careful discussion of benefits versus risks. Women should have this information, as well as information about other options that do not involve hormonal contraception, such as intrauterine devices without hormone release, tubal ligation, and vasectomy for their partner.

Thank you so much for your attention. This is JoAnn Manson.


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