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

Leslie Hanson
December 7, 2017

Using hormonal birth control methods - including newer types of birth control pills, as well as intrauterine devices (IUDs) and implants - may slightly increase women's risk of breast cancer, according to a new study from Denmark.

While contraceptive drugs that contain oestrogen have always been suspected of increasing the likelihood of breast cancer, researchers had expected smaller doses of the hormone, often combined with the drug progestin, would be safer, said Lina Morch, an epidemiologist at Copenhagen University Hospital who led a study analysing the records of 1.8 million women in Denmark.

Compared to what the group of researchers found in one of their other papers-that using hormonal contraception was associated with a 300 percent increase in suicide risk-"it is a modest increase", said Dr. Øjvind Lidegaard, one of the authors of the paper and a gynecologist at the University of Copenhagen.

"In the 1980s and 1990s, there was some optimism regarding the development of a formulation that would reduce a woman's risk of breast cancer", he said in the commentary, "but research into this possibility appears to have stalled".

Other studies have shown hormonal birth control may lower the risk for ovarian and endometrial cancer. "But we should make an individual assessment-doctor and a woman, together-to see what is the most appropriate thing for her to use". Another way of looking at that is that there would be one additional case of breast cancer each year among 7,700 people who use hormonal 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.

And the latest study only showed an association - it did not prove that taking the newer versions of the pill actually caused breast cancer risk to rise.

Shirazian notes that for women of average risk of breast cancer, the concern is not high. As research began to link estrogen to breast cancer, the FDA took off the market any formulations that had more than 50 micrograms of estrogen, Gaudet said. They also contain progestin, a synthetic form of the female hormone progesterone, which helps regulate the monthly menstrual cycle.

The new study looked at all women in Denmark ages 15 to 49 who had not had cancer, clots in their veins, or treatment for infertility.

Breast cancer is the second-biggest cancer killer of American women, after lung cancer.

Duration of use also contributed to associated breast cancer risk.

In fact, birth control increases breast cancer risk about as much as drinking alcohol does, said Dr. Mary Beth Terry, an epidemiologist at the Columbia University Mailman School of Public Health. In the meantime, women who are using oral contraceptives might want to speak to their doctors about use before age 35 and after age 35. "It has been known that progesterone probably plays a role in breast cancer, although our research is not as mature as it is for estrogen".

The data are "a gold mine for doing these kinds of analyses", she said.

Mørch explained to MedPage Today that "there was a lack of evidence on contemporary hormonal contraception and risk of breast cancer".

The study is published today (Dec. 6) in The New England Journal of Medicine.

For more on oral contraception, visit the U.S. Department of Health and Human Services.

Other reports by Iphone Fresh

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