Recently, a patient I have known for many years asked about the risks of taking birth control pills for an extended period of time. Her older sister had recently been diagnosed with breast cancer, and my patient was worried that she might be increasing her risk of cancer herself.
This patient is in her late 30s and has been taking birth control pills since her teens. She started them to manage heavy periods and continued taking them for contraception and convenience. Her withdrawal bleeds (essentially a “period” that occurs while taking the sugar pills) were short and light. And if she expected a withdrawal bleed during a vacation or a busy week at work, she would just skip the sugar pills and start a new pack.
But for all the convenience of taking birth control pills, she was prepared to stop them and switch to a non-hormonal form of contraception if she found out they were putting her at risk for cancer.
Is there a connection between hormonal contraception and breast cancer risk?
Over the years, there have been many studies trying to find the answer to this question. Many of those studies were small retrospective studies, and the results were mixed. Older studies often included patients taking high-dose birth control pills, with many times the estrogen dose of modern birth control pills, as well as different forms of progestin. Most only included women using birth control pills, not other delivery methods such as patches, rings, IUDs, and implants. Previous studies also lumped together women with premenopausal and postmenopausal breast cancer.
In 2017, a study that sought to deal with a lot of the issues found in previous studies was published in the New England Journal of Medicine. The Danish Sex Hormone Register study began in 1995 and collected data regarding nearly 1.8 million women’s use of hormonal contraception of all types for nearly 20 years.
The researchers not only knew which women used hormonal contraception and which did not, but also what method(s) of contraception the women used, the doses of estrogen and progestin, and when and how long the women used hormonal contraception. The authors then used data from the Danish Cancer Registry to confirm whether or not the women in their cohort had been diagnosed with breast cancer.
They found that among all women who had used hormonal contraception, there was about a 20% increase in breast cancer diagnoses compared with the women who had never used hormonal contraception. This may sound alarming at face value, but because of the size of the study, they were able to dig much deeper into the subtleties in the data. In doing so, they found that women who used hormonal contraception for fewer than five years had no increased risk of being diagnosed with breast cancer. Among women who had used hormonal contraception for more than five years, the risk of breast cancer increased with longer use.
Does the type of hormonal contraception matter?
The researchers in the above study found that the dose of estrogen in birth control pills did not change breast cancer risk significantly. There was no clear benefit to taking lower-dose pills compared with higher-dose pills. Estrogen does seem to increase the risk of breast cancer compared with progestin alone. But progestin-only pills and progestin-eluting IUDs were also associated with a small increased risk of breast cancer.
The researchers did not find a difference in breast cancer risk between birth control pills with different doses of estrogen and progestin over the course of the pack compared with those with the same doses throughout the pack. They also didn’t find differences between different types of progestins. The risks of breast cancer in patients using progestin-eluting IUDs was similar to the risk associated with progestin-only birth control pills. How the progestin was delivered did not appear to affect a woman’s risk.
Should you stop taking hormonal contraception?
Before you toss your birth control pills in the trash or have your IUD removed, it is important to note that while there were relative increases in breast cancer risk, the overall risk of breast cancer among this group of women — who were between the ages of 15 and 49 at the time of enrollment in the registry — was quite small.
Premenopausal breast cancer is rare. About 65 in 100,000 women will be diagnosed with premenopausal breast cancer. Using hormonal contraception for more than five years increases that number by 13, to just 78 in 100,000. In fact, there was only one additional breast cancer diagnosis for every 7,690 women using hormonal contraception for one year.
The increased risk of breast cancer with birth control pills seems to disappear about five years after the pills are stopped. And the risk of breast cancer after menopause — the most common time for breast cancer to be diagnosed — does not appear to be increased with past use of hormonal contraceptives.
Additionally, use of birth control pills is associated with a long-term reduction in endometrial cancer. In women with BRCA gene mutations, putting them at high risk for breast and ovarian cancer, birth control pills reduce ovarian cancer risk.
Ultimately, a statistically significant, but very small, increase in premenopausal breast cancer is just one consideration among many when it comes to choosing a contraceptive method. So many other factors come into play. Hormonal contraception is highly effective at preventing unwanted pregnancy. Some health problems, such as anemia from heavy periods, are often effectively treated with hormonal contraception. And personal preference — using a form of contraception that works well for you — matters.
The bottom line
- Studies have found a very small but statistically significant increase in premenopausal breast cancer among women who have used hormonal contraception for more than five years.
- Postmenopausal breast cancer risk does not appear to be increased with past hormonal contraceptive use.
- Birth control pills reduce the risk of endometrial cancer even many years after a woman stops taking them, and they may reduce the risk of ovarian cancer among women at high risk of developing ovarian cancer.
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