A major new study has found that even birth control pills and other contraceptives that release low doses of hormones increase the risk of breast cancer in women.
While the link between hormonal birth control and breast cancer has been known for years, many doctors and women had hoped that newer forms of birth control, such as IUDs, vaginal rings and implants, put women at less risk.
The study by researchers from the University of Copenhagen, which followed 1.8 million Danish women for more than a decade, found that differences in the formulation of hormone-based birth control had little effect on the cancer risk. The study also found that the risk of cancer increased the longer a woman used the birth control.
Overall, the breast cancer risk was 20 percent higher for women who were currently using or had recently used hormonal contraceptives than among those who had never used it. The estrogen used in hormonal contraceptives can promote the development of breast cancer.
“As compared with women who had never used hormonal contraception, an increased risk of breast cancer was observed among women who had previously used hormonal contraception for a long period of time,” the researchers wrote in the study released this week in The New England Journal of Medicine.
For women who have used birth control for long periods, the increased risk of cancer may continue for five years after they stop using it, the researchers found. The risk for getting breast cancer was 9 percent higher for women who used birth control for less than one year and 38 percent higher for those who used it for more than 10 years.
The study offered a look at the effects of modern birth control use, over a long period of time, in a large group of women. The researchers followed women between the ages of 15 and 49 over an average of nearly 11 years.
Sixty-two percent of women of reproductive age use contraception, according to a report by the National Center for Health Statistics that looked at the period from 2000 to 2010. Most women used birth control pills, the report said.
About 255,000 women in the United States are expected to be diagnosed with breast cancer in 2017 and about 41,000 are expected to die from it, according to the American Cancer Society.
The study raised concerns for some Baltimore-area gynecologists, who said women should consult with their doctors if they were worried about the correlation, particularly if they already had other risk factors for breast cancer.
“The risks and benefits should be discussed,” said Dr. Katherine Tkaczuk, a professor of medicine at the University of Maryland School of Medicine and director of the breast evaluation and treatment program at the University of Maryland Marlene and Stewart Greenebaum Comprehensive Cancer Center. “I certainly wouldn’t want people to stop taking birth control. Most doctors think there are many benefits to birth control. Women just need to be aware of the risks.”
Birth control has also been linked to lower incidences of uterine, endometrial and colon cancers later in life. It can also help women who have heavy cramps and menstrual bleeding.
Dr. Mahsa Mohebtash, a medical oncologist and the director of The Cancer Center at Medstar Union Memorial Hospital, said the study raised real concerns.
Mohebtash said that some women might want to consider other forms of birth control that don’t use hormones, such as condoms. Some IUDS also don’t use hormones, she said. Women who don’t want to get pregnant in the future also can undergo tubal ligation.
“Even if they want to continue on birth control they need to at least know the risks so they can be more vigilant,” she said.
Dr. Dona Hobart, medical director of the Center for Breast Health at Carroll Hospital, said that women have to make a similar decision when deciding whether to take hormone replacement therapy, which also can increase the risk for breast cancer.
“I do encourage people to talk with their doctor and not go running off their birth control,” Hobart said.
The researchers who conducted the study said it was limited because it did not look at other factors, such as when study participants first started menstruating, their level of physical activity, or the amount of alcohol they consume — all factors that might promote the development of breast cancer.
The study also looked at younger people, when older people are more often diagnosed with cancer, Hobart said.
The American College of Obstetricians and Gynecologists said in a statement that it was taking the results of the study “very seriously.” However, it expressed some reservations about the findings.
“While this study raises known associated risks between breast cancer and hormonal contraception, we believe a robust evaluation of the study, including the study design, is necessary to accurately interpret the findings and reach conclusions,” Dr. Chris Zahn, a vice president with the organization, said in a statement. “This should include consideration of other factors that have significant impact on the findings, including family history of breast cancer for both pre- and post-menopausal women, stage of disease and morbidity or mortality from the breast cancer diagnoses.”
Zahn said there also needs to be comparisons of outcomes for women using hormonal contraception to outcomes for pregnant women, to create a complete picture of the risks attendant to both circumstances. Such a study would be useful, he said, to show that hormonal contraception, “risks and all,” may be essential to preventing pregnancy in some women with high risk for other medical conditions, such as diabetes.
In an editorial that accompanied the study, Dr. David Hunter of the University of Oxford wrote that the search should continue for birth control that doesn’t increase the risk of breast cancer.