Hormonal birth control raises breast cancer risk slightly: study

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Both progestin-only and combined hormonal birth control slightly raises the chances of getting breast cancer, a new study with the University of Oxford found, but the overall risk remains low.

The study, published in PLOS Medicine, found that new forms of progestin-only hormonal birth control carry a small increased risk for breast cancer as well as combined contraceptive pills which contain both progestin and estrogen ingredients.

"There’s quite a lot of evidence already that women have an increase in breast-cancer risk while they’re taking combined oral contraceptives," Gillian Reeves, director of the cancer epidemiology unit at the University of Oxford and an author of the study told the TIME. "That increase is small, and it seems to decline once women stop taking it.

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PLOS Medicine, researchers found that taking progestogen-only birth control comes with a 20% to 30% increase in breast cancer risk, which is similar to its combination counterpart with estrogen.

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While 20% to 30% is a large number, Reeves maintains that the average's woman's chances of developing breast cancer, if she has no other indicators or family history—is very small to begin with. 

"Twenty percent is not going to lead to many extra cases, because it’s so rare," Reeves told the TIMES.

Blister packs containing Femoden oral contraceptive tablets, produced by Bayer AG, sit on a pharmacy counter. (Chris Ratcliffe/Bloomberg via Getty Images)

Although breast-cancer risk increases as women age, "for women who, say, take it for five years from 30 to 34, you’re talking about an increase in risk up to age 50 of something like 0.2%," Reeve said. "So it’s very small."

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The researchers analyzed data from 9,488 women who were between 20-years-old and 49-years-old who developed invasive breast cancer and 18,171 "closely matched controls" of women without breast cancer. 

They found that 44% of the women with breast cancer and 39% of the women without it had been prescribed a hormonal contraceptive an average of three years before their diagnosis. About half the prescriptions were for progestagen-only birth control pills.

The study also noted that the method of taking birth control, whether it be by pills orally, patches, implants and injections, all carry the same amount of risk.

Holding an IUD birth control copper coil device in hand, used for contraception - side view (iStock)

They also found that hormonal birth control is associated with protection against endometrial and ovarian cancers, which unlike the increased breast cancer risk, doesn't go away after birth control is stopped.

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"Such risks need be balanced against the benefits of using contraceptives during the childbearing years," the study noted in the conclusion.