We Now Know More About the Link Between Birth Control & Breast Cancer

Katherine Streeter for NPR

Enlarge this image Katherine Streeter for NPR Katherine Streeter for NPR

Whether it's the pill, the patch, or a range of other products, millions of women today use hormonal contraceptives; so it's little surprise that a new study shows that those who take them have an increased risk of breast cancer.

Overall, the use of any hormone-based contraceptive for five years or more raised a woman's risk of breast cancer by 20 percent, Lina Morch of the University of Copenhagen and colleagues reported in the New England Journal of Medicine.

One thing reiterated by every doctor Newsweek spoke to: Women who are anxious about how their contraception might increase their risk of breast cancer should speak with their health care provider.

The new paper estimated that for every 100,000 women, hormone contraceptive use causes an additional 13 breast cancer cases a year.

Breast cancer is the second-biggest cancer killer of American women, after lung cancer. And for those who take the drugs for five years or more, the risk will persist for as long as five years after they stop, she said. "Taking a very low absolute risk and increasing it only slightly is still a relatively low risk".

A hormone specialist at Brigham and Women's Hospital who deals with contraceptive issues says the study shouldn't alarm those taking oral contraceptives. Women who used any form hormonal contraception for more than 10 years (1.38, 95% CI 1.26-1.51) had a higher risk compared to those who reported less than 1 year of use (1.09, 95% CI 0.96-1.23)(P=0.002), they wrote online in the New England Journal of Medicine.

The study, which used all of Denmark as its sample, followed almost 1.8 million women of childbearing age for over a decade on average, drawing data from national prescription and cancer registries.

They include smoking, obesity, starting menstruation early, having children late in life or not at all and not breastfeeding.

Experts noted that oral contraceptives have some benefits as well, and are associated with reductions in ovarian, endometrial and possibly colorectal cancers later in life.

"There were hopes that the new formulations would not increase a user's risk of breast cancer as the older formulations did", said Mia Gaudet, strategic director of breast and gynecologic cancer research at the American Cancer Society, who was not involved in the research.

Researchers found a similar breast cancer risk with the progestin-only intrauterine device.

Lindegaard speculated that the hormones in birth control may trigger certain cells that are ready to turn into cancer, he said, given that the risk seems to increase after only a few months of use.

"Estrogen has been the primary focus of breast cancer research in general, and so we know much more about it than we do progesterone", Gaudet said.

"Progestin-only products also increased the risk of breast cancer", Morch noted.

Even if the relative risk increases 20 per cent, it remains less than one-tenth of 1 per cent. However, it was commonly thought that the newer low-dose estrogen options significantly decreased - or even eliminated - that risk. "That is not a huge risk increase", she told NBC News.

In Denmark, older women who have completed their families are most likely to use IUDs, including those containing hormones, and they are already more likely to develop breast cancer because of their age, Mørch said. That roughly translates to a 12 percent lifetime risk for a woman, although many factors affect breast cancer risk.

IUDs infused with hormones also appear to pose a risk, Morch said, so "so there's a lot of things to take into account when deciding what type of contraception to use".

Not only that, but there are plenty of non-hormonal birth control options to consider, like the non-hormonal IUD, diaphragm and condoms - and let's not forget vasectomies.

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