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Hormonal Birth Control and the Risk of Breast Cancer

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Hormonal Birth Control and the Risk of Breast Cancer

Dec 21, 2017

Low-dose methods of contraception, such as birth control pills, IUDs, and implant, have been found to increase the risk of breast cancer in women. Dr. Kirtly Parker Jones talks about these new findings from a Denmark study, the benefits and risks of hormonal birth control, and what it could mean for you.

Episode Transcript

Dr. Jones: New news and old news about the risk of breast cancer and hormonal birth control. Get ready for some really very big and very small numbers. This is Dr. Kirtly Jones from Obstetrics and Gynecology at University Health and this is The Scope.

Announcer: Covering all aspects of women's health. This is The Seven Domains of Women's Health with Dr. Kirtly Jones on The Scope.

Dr. Jones: Today we're going to talk about hormonal birth control and the risk of breast cancer. Primarily, we'll talk about birth control pills, but we'll also talk about hormonal patches, shots, implants, and IUDs. There are now 50 years of data on the topic of hormonal birth control pills and the risk of breast cancer. Largely, the studies have suggested that there's no significant increased risk of breast cancer in birth control pill users except maybe in women who used pills starting early in their teens, used them for a long time, and use them into their 40s. Recently, a study from Denmark looked at 1.8 million women between the ages of 15 to 49 who had used hormonal contraception between 1995 and 2012. They were using contraceptive methods that are commonly prescribed today. Because Denmark has a health system that can follow everyone and link diagnosis with prescriptions and health outcomes, they can really do big studies.

So what did they find? First, the extra risk of breast cancer in women of this age group who took hormonal birth control of any type during this time period was 13 extra breast cancers per 100,000 women per year. That's a very small number, 13, out of a pretty big number, 100,000. That is, for every 100,000 women using hormonal birth control, there are 68 cases of breast cancer annually compared to 55 cases a year among non-users. Another way to crunch these numbers is to say there was one extra breast cancer for every 7,690 women using hormonal contraception.

Of course, the details are a little more interesting. For the users of hormonal patches, the extra breast cancers were 5 per 100,000, but it ranged from 1 fewer and 11 more, and essentially it wasn't different from women not using hormonal birth control. Maybe there are just weren't as many women taking it. It's not clear, because the hormonal patch is kind of like the hormonal pill.

For women using vaginal rings, there were two fewer breast cancers. But the statistical range was 32 fewer to 28 more. So there wasn't any increased risk in this group.

The same kinds of numbers were seen for women using contraceptive implants or injections. There were about 5 to 10 fewer breast cancers, but the ranges were so large that there really wasn't an increase or a decrease.

Hormonal IUD users had about the same increase as pill users with about 16 extra breast cancers per 100,000 women. Importantly, and listen to this, the risk for women under 35 years of age was 2 extra breast cancers per 100,000 women per year, a really small number. Young women had a lower risk of breast cancer on hormonal contraception than older women. And women who had used hormonal contraception for a long time, meaning 10 years or more, had a slightly larger absolute risk than women who only used it a short time.

So what do we do with these numbers? First, don't panic. Every time there's bad news about contraception, even if it's barely bad, women stop their contraception and the unplanned pregnancy rate and abortion rate goes up. Now there, you're really taking some risks. It is really hard to know how to counsel women about a risk that is one extra per 7,960 women. Those are numbers that people don't really understand very well. Also, people really don't like numbers like 7,960. They like 10 or 1,000.

So I consider a significant risk is 1 extra in 10. A low risk is 1 extra in 100. A very low risk is 1 extra in 1,000, and an extremely low risk is 1 extra per 10,000, and that's really what we're talking about. The authors of this study admit that they didn't control for age of first period in these ladies, alcohol consumption, breastfeeding, and physical activity. All of these activities increase or decrease the risk of breast cancer by a little. Breastfeeding decreases the risk of breast cancer, and certainly women who breastfeed are less likely to use hormonal birth control. So that could be part of why there was a slight increase in hormonal birth control users.

Now, there's something called biological plausibility. In population studies, they'd find a correlation of one thing with another. Let's pick alcohol. People who drink alcohol moderately live longer. People who drink alcohol a lot don't live so long. Now, is it the alcohol that makes you live longer? Or is it the people who drink alcohol have more fun, have more friends, and having friends makes you live longer? So this is a biological plausibility issue.

Is there a biological reason that hormonal contraception might very slightly increase the risk of breast cancer? Over the past 20 years, researchers have been more interested in the progestin component of the hormonal contraception and menopausal hormone replacement therapy. We always thought that the risk for breast cancer was all about estrogen, but progestin, that other hormone in hormone replacement or in hormonal birth control, seems to add a little risk as well. So there's a possible biological reason for this very small increase in breast cancer in hormonal contraception users.

The authors of this study also suggest that women don't panic, but they didn't exactly say that. They mentioned that hormonal birth control pills have substantial health benefits. Birth control pills substantially decrease the risk of uterine and ovarian cancer and possibly colon cancer. In fact, women who have the BRCA gene for breast and ovarian cancer have been suggested to take birth control pills because even if the risk of breast cancer is slightly greater, the risk of ovarian cancer, a cancer that's hard to detect and hard to treat, is so much less on birth control pills.

So what should you do? We all know that hormonal contraception comes with risks and benefits. For the vast majority of us, the ability to control when and how often we have children is a fundamental factor in our ability to manage our lives. Many women use hormonal birth control, such as hormonal IUDs, to manage flooding periods and pain that debilitates them every month.

If these recent findings are a major concern for you, talk to your clinician about the risks and benefits for you personally. Not you in 100,000 women. Put things in your own personal perspective. There are options for us, probably more than you know, and thank you for joining us on The Scope.

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