Even low-dose contraceptives slightly increase breast cancer risk

It's long been known that hormonal contraception, like any medicine, carries some risks. But doctors and women have hoped that the newer generations of low-dose contraceptive pills, IUDs and implants eliminated the breast cancer risk of earlier, higher-dose formulations.

Now a big study from Denmark suggests the elevated risk of getting breast cancer — while still very small for women in their teens, 20s and 30s – holds true for these low-dose methods, too. In the research published Wednesday in the New England Journal of Medicine, a team of scientists studied 1.8 million women between the ages of 15 and 49. They were looking to see what happened over a stretch of nearly 11 years among women who used hormonal birth control — usually a combination of estrogen and progestin — versus women who relied on non-hormonal contraceptive methods, such as a condom, diaphragm or copper IUD.

Unlike most previous research, this study didn't just track the effect of birth control pills. Because their set of data was very large, scientists this time were also able to get a good sense of the impact of various other hormonal methods — including the birth control patch, the ring, and implants as well as hormone-releasing IUDs.

The results showed it didn't much matter what sort of hormonal method was used, says Lina Morch, a research epidemiologist at the University of Copenhagen, who led the study.

Overall, Morch says, she and her colleagues found "a roughly 20 percent increased risk [of breast cancer] among women who currently use some type of hormonal contraception." And the longer the women used hormonal methods, she says, the higher their risk.

That may sound scary. But Morch and other doctors say it's important to consider how that additional risk translates in terms of actual cases of breast cancer. The illness is fairly rare among women in the age group studied.

"A 20 percent increase of a very small number is still a very small number," says Mia Gaudet, an epidemiologist with the American Cancer Society. The risk contributed by hormonal contraception, she says, is similar to the extra breast cancer risk contributed by physical inactivity, excessive weight gain in adulthood, or drinking an average of one or more alcoholic drinks per day. "The absolute increase in risk [found in the study] is 13 per 100,000 women overall, but only 2 per 100,000 women younger than 35 years of age," writes epidemiologist David Hunter, of the University of Oxford, in an editorial accompanying the study in NEJM.

"Most of the cases that occurred in this analysis occurred among women who were using oral contraceptives in their 40s," Hunter adds.

Any additional risk of breast cancer, he says, should be weighed against the clear benefits of hormonal contraception — benefits that go beyond the obvious advantages of preventing unwanted pregnancy.

"There's very good evidence," Hunter says, "that oral contraceptives reduce the risk of ovarian cancer. They reduce the risk of endometrial cancer. And there's a strong suggestion they also reduce the risk of colorectal cancer. So, many calculations suggest that the use of oral contraceptives actually prevents more cancers than it causes."

The search for new hormonal contraceptives — methods that don't elevate breast cancer risk at all — should continue, Hunter says.

Meanwhile, a conversation with your doctor can help you figure out which contraceptive method makes most sense for you. Copyright 2019 NPR. To see more, visit https://www.npr.org.