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Birth control and breast cancer risk among younger women

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On December 7, 2017 the New England Journal of Medicine published results from a study by Lina Mørrch of the University of Copenhagen and colleagues showing that hormonal contraceptives (birth control) increase the risk of breast cancer. The study is unique because it is one of the first to specifically assess the breast cancer risk associated with newer, low-dosage methods of contraception. The large and significant effort analyzed medical data of nearly 1.8 million young women in Denmark on average for over 10.9 years. Results were covered widely in the U.S. by many major media outlets, including the New York Times, USA Today, Forbes and Time.  (12/14/17)



This study is about:

Lower-dose hormonal contraceptive use affects younger womens’ risk for breast cancer.

Why is this study important?

Effective and available, birth control is an important priority for many women around the world, including about 10 million women in America. Aside from the obvious benefit, birth control pills help to control acne, PMS, heavy periods and mood swings. Research also shows that oral contraceptives offer preventive benefits as well: slightly lower risks of ovarian, endometrial and possibly colon cancer. 

Convenient, reliable and affordable, birth control pills have been used by women for more than 50 years. But are they safe? The pills release hormones, usually a combination of estrogen and progesterone, to block pregnancy by preventing ovulation. These additional hormones, especially estrogen, have long raised concerns about increasing risk for breast cancer. Studies in the 1980s found that hormone levels in birth control pills stimulated breast cells and increased risk. Newer generation oral contraceptives with lower amounts of hormones have been assumed to equate to fewer side effects, including a lower risk of breast cancer. This study tested that hypothesis among young women.

Study findings: 

Similar to their older counterparts, newer, low-dose birth control pills were found to slightly raise a woman’s risk of breast cancer: the absolute overall increased risk was 1 additional case in every 7,690 women using hormonal contraception for 1 year. Hormone-infused devices such as vaginal rings, implants and some IUDs also slightly increased risk. Longer use equated to increased risk. Overall, using any hormone-based contraceptive for 5 years or more raised a young woman’s risk of breast cancer by 20 percent.

What does this mean for me?

Until recently, many women (and their doctors) believed newer hormonal contraceptives to be safer than those taken by their mothers or grandmothers, which released higher doses of estrogen. This study shows that contemporary low-dose birth control pills do slightly increase breast cancer risk in average risk women, but the absolute risk is small, especially when weighed against the known benefits of oral contraceptive use. (Risk differs depending on personal behavioral and environmental factors, and it increases as a woman ages.) The potential breast cancer risk identified in this study must be balanced by the need for reliable contraception in this age group. 

This study did not specifically look at risks in women at high risk for breast cancer due to a BRCA or other mutation. Prior data on oral contraceptive use and breast cancer risk specifically in BRCA mutation carriers is not clear particularly for early exposure (teens and early 20s). Retrospective case control studies show no impact but all prospective studies actually do show an impact. Generally, prospective studies are considered to be more informative than retrospective studies. 

For mutation carriers, meta-analysis from 2014 concluded that case control studies did not show an association between BRCA1 mutation status and oral contraceptive use and breast cancer but cohort studies did.  The combined cohort studies revealed an increased relative risk of 1.5 which can be significant for mutation carriers whose risk is already quite high. Similar findings were found for BRCA2 and breast cancer risk.

The data on oral contraceptive use and ovarian cancer shows that oral contraceptive use for at least 6 years lowers the risk of ovarian cancer for BRCA1 and BRCA2 mutation carriers. For woman at significantly increased risk of ovarian cancer due to inherited mutations, the benefits of oral contraceptive use may outweigh the slight increase in breast cancer risk.

Questions to ask your health care provider:

  • I’m currently taking birth control pills; do I need to switch to some other type of contraceptive?
  • What are my options for non-hormonal contraceptive options?
  • Does my IUD contain progestin? Is there another, effective type of IUD that does not?
  • Given my risk for both breast and ovarian cancer, do the benefits of oral contraceptives outweigh the risks?

Study background:

This prospective study followed more than 1.8 million women in Denmark for over a decade.  Data was collected from medical visits and prescription drug purchases.

Researchers of this study wanted to know:

Whether newer, low-dosage hormonal contraception increases the risk of breast cancer.

Population(s) looked at in the study:

Researchers analyzed the health records of nearly 1.8 million Danish women between ages 15 and 49 who had not had cancer or venous thromboembolism and who had not received treatment for infertility for almost 11 years. They compared women who purchased birth control methods to women who developed breast cancer.

Study findings: 

Women who relied on contemporary, low-dose birth control pills or contraceptive devices that release hormones had a small but significant increase in breast cancer risk, similar to the risk from older types of contraceptive pills. However, the increase in absolute risk of breast cancer was small—an additional diagnosis was made among 1 in every 7,690 women who used hormonal contraception for 1 year. Longer use equated to greater risk. Increased risk ranged from 9 percent among women who used birth control pills for a year or less to 38 percent for women who used the pills for 10 years or more. Overall, the use of any hormone-based contraceptive for 5 years or more raised a woman’s risk of breast cancer by 20 percent.

Another important and worrisome finding involved intrauterine devices (IUDs) that dispense the hormone progestin. Compared to women who did not use an IUD, women who used an IUD that contained progestin were 21 percent more likely to develop breast cancer. Although estrogen is known to raise breast cancer risk, this finding suggests that progestin alone, which is released from some contraceptive pills and some IUDs, also raises that risk. Sometimes, an IUD with progestin is used for women who want to keep their uterus after stopping oral contraceptives to balance estrogen replacement therapy to minimize systemic progestin exposure. This study implies that this alternative may also carry risk.


The study could not take into account certain factors, including physical activity, breastfeeding and alcohol consumption, which may also influence breast cancer risk. The population studied was predominantly Caucasian so it is not known how much these results would extend to women of other races.

This study only adjusted for a family history of premenopausal breast cancer or ovarian cancer.  Women with any family history of breast or ovarian cancer might be less likely to use hormonal contraception which would result in an underestimation of breast cancer risk for these women.

This research was supported by a grant from the Novo Nordisk Foundation, a self-described “independent Danish foundation with corporate interests” that supports medical research at public institutions, and by companies within the Novo Group. (Novo Nordisk is a global health care company that focuses on diabetes care. It also makes Vagifem, topical estrogen inserts designed for menopausal women.)

A postscript to the article disclosed that two of the study authors have been employed by Novo Nordisk since the manuscript was accepted for publication.


The risk of breast cancer was higher among women who used newer, low-dosage hormonal contraceptives than among women who had never used hormonal contraceptives. However, absolute increases in risk were small. This risk increased with longer durations of use. Increased risk was also was seen in women using implanted intrauterine devices (IUDs) containing the hormone progestin.

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Posted 12/14/17


Mørch LS, Skovlund CW, Hannaford PC, Iversen L, Fielding S and Lidegaard Ø. Contemporary Hormonal Contraception and the Risk of Breast Cancer. N Engl J Med. 2017. 7;377(23):2228-2239.

National Cancer Institute: Oral Contraceptives and Cancer Risk  

Related Information and Resources

FORCE: Breast Cancer Risk

FORCE: Ovarian Cancer Chemoprevention

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