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Is There a Link Between Birth Control Pills and Higher Breast Cancer Risk?

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The need for safe, effective birth control is shared by many women around the world. More than 10 million American women use birth control pills. Besides effectively stopping unwanted pregnancies, birth control pills also help control other conditions, such as acne, PMS, heavy periods, and mood swings. Research also has shown that birth control pills can slightly lower the risk of uterine and ovarian cancer.

Effective, uncomplicated birth control is important for many women. But it’s also important that birth control be safe. There are concerns that because birth control pills use hormones to block pregnancy they may overstimulate breast cells, which can increase the risk of breast cancer.

The concern is greater if you’re at high risk for breast cancer because of:

  • a strong family history of the disease
  • past breast biopsies showing abnormal cells
  • you or someone in your family has an abnormal breast cancer gene

If you’ve been diagnosed with breast cancer, you SHOULD NOT use contraceptives that use hormones. That’s because there’s evidence that these medicines might increase the risk of the cancer coming back (recurrence).

A study looked at whether recent use of birth control pills is linked to a higher risk of breast cancer in women ages 20 to 49. The results found that using high-dose estrogen birth control pills in the previous year was linked to a higher risk of breast cancer in these younger women, but using birth control pills with a low dose of estrogen (the type of birth control pills that many women take) WAS NOT linked to a higher risk of breast cancer.

The study was published in the Aug. 1, 2014 issue of Cancer Research. Read the abstract of “Recent Oral Contraceptive Use by Formulation and Breast Cancer Risk among Women 20 to 49 Years of Age.”

You may have heard or read about this story in the media. In most cases, the reports only talked about birth control pills increasing risk and didn’t explain that it was only high-dose estrogen birth control pills. It’s important to know all the details of the study before you draw any conclusions.

The debate about birth control pills and breast cancer isn’t new. Researchers have been looking at the issue for many years, but the results have been mixed:

  • A review of 54 studies in 1996 found that women have a slightly higher risk of breast cancer while they’re taking birth control pills that contain both estrogen and progestin and during the 10 years after they stop taking the pills. Progestin-only pills also increased risk, but not as much.
  • The large Women’s Contraceptive and Reproductive Experiences Study, published in 2002, found that current or past use of birth control pills didn’t increase the risk of breast cancer in women aged 35 to 64. But the researchers noticed a small increase in risk among women aged 35 to 44 who used birth control pills and had a family history of breast cancer.
  • Results from the Nurses’ Health Study released in 2010 found that past use of any birth control pill was not linked to breast cancer risk. But the results also suggested that current use slightly increased risk. The higher risk occurred mostly among women taking triphasic pills – pills that have different doses of hormones over three stages of the monthly cycle.
  • A 2012 analysis of the research on risk factors for breast cancer in women aged 40 to 49 found that current use of hormonal contraceptives slightly increased risk.

In this study, the researchers looked at the records of more than 23,000 women who were enrolled in a healthcare delivery system in the Seattle area. All the women were age 20 to 49 and had been enrolled in the healthcare system for at least a year. The researchers defined “recent use” of birth control pills as taking the pills within the previous 12 months.

The researchers matched 1,102 women who’d been diagnosed with breast cancer to 21,952 women who hadn’t been diagnosed by age, the length of time they had been enrolled in the healthcare system, and the availability of their medical charts.

The researchers also looked at the type of birth control pills the women were taking, including the dose of hormones and monophasic or triphasic types of pills. Instead of relying on the women remembering what type of birth control pills they took, the researchers looked at the women’s electronic pharmacy records.

Overall, the researchers found that women who had used birth control pills within the previous year had a 50% increase in the risk of breast cancer compared to women who had never or had formerly used birth control pills.

While these results sound very alarming, it’s important to know three things:

  1. This risk varied with the formulation of the birth control pills:
    • high-dose estrogen birth control pills more than doubled the risk of breast cancer
    • ethynodiol diacetate (a type of progestin) birth control pills also more than doubled the risk of breast cancer
    • triphasic birth control pills with an average dose of 0.75 mg of norethindrone (a type of progestin) more than tripled the risk of breast cancer
    • other types of birth control pills, including low-dose estrogen pills, WERE NOT linked to a higher risk of breast cancer
    Only a small number of women in the study were using high-dose estrogen pills:
    • 24% of the women were using low-dose estrogen pill
    • 78% were using moderate-dose estrogen pills
    • less than 1% were using high-dose estrogen pills
  2. This increase in risk is relative risk. Relative risk tells you how much something you do, such as maintaining a healthy weight, can change your risk compared to your risk if you're very overweight. Relative risk can be expressed as a percentage decrease or a percentage increase. If something you do or take doesn't change your risk, then the relative risk reduction is 0% (no difference). If something you do or take lowers your risk by 30% compared to someone who doesn't take the same step, then that action reduces your relative risk by 30%. If something you do triples your risk, then your relative risk increases 300%.

    Any increase in relative risk needs to be multiplied by a woman’s absolute risk to figure out her real risk.

    Most experts agree that an average woman younger than 50 with no family history of breast cancer and no abnormal breast cancer genes has an absolute risk of breast cancer that is less than 2%. So if that risk doubled, it would still be less than 4%.
  3. This study didn’t take into account whether the women had any family history of breast cancer or had an abnormal BRCA1 or BRCA2 gene. This is HUGELY important and has made some other researchers question the results of the study. This is because we already know that women with a family history of breast cancer or who have an abnormal BRCA1 or BRCA2 gene shouldn’t take birth control pills. Since the researchers didn’t account for these factors, it’s impossible to know how much they influenced the results.

Even the study’s lead researcher, Elisabeth Beaber, of the Fred Hutchinson Cancer Research Center in Seattle, said the results require confirmation.

“Our results should be interpreted cautiously,” she said. “Breast cancer is rare among young women and there are numerous established health benefits associated with oral contraception use that must be considered. In addition, prior studies suggest that the increased risk associated with recent oral contraceptive use declines after stopping oral contraceptives.”

If you’re a healthy younger woman with an average risk of breast cancer (no family history and no known abnormal breast cancer genes in your family), then taking birth control pills is considered relatively safe for you. If you would like to use birth control pills for contraception, ask your doctor about an effective low-dose estrogen pill.

When your risk is higher for any reason, including being older, then you need to be more careful and avoid anything that could make that risk even higher, including birth control pills. That’s why birth control pills aren’t recommended for women who’ve been diagnosed with breast cancer.

If your breast cancer risk is higher than average for any reason, talk to your doctor about alterative birth control methods. Condoms, diaphragms, and non-hormonal intrauterine devices (IUDs) such as ParaGard all may be options for you.

No matter which type of birth control you use, ask your doctor if you have any questions about how to use it effectively.

For more information on birth control methods that don’t use hormones, read Chief Medical Officer Dr. Marisa Weiss’s “Alternatives to the Pill” Think Pink, Live Green column.

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