, was previously linked to a small increase in breast cancer risk. In recent times, forms of birth control containing only progestogen have become more popular.
In a study published in the journal PLOS Medicine, researchers show that taking progestogen-only birth control comes with a 20% to 30% increase in
risk, which is similar to its combination counterpart. The baseline risk of developing breast cancer is low, especially among young people, so this represents a relatively small increase in the overall risk.
While the pill protects against other cancers like ovarian cancer, the new data can help people make more informed decisions about whether to take hormonal birth control, considering both its risks and benefits.
While it is well known that combined oral contraceptives are associated with a small, transient increase in breast cancer risk that declines after stopping use, less is known about progestogen -only contraceptive use.
The researchers looked at data from the Clinical Practice Research Datalink, a database made up of healthcare information from the U.K. National Health Service. They examined a group of about 9,500 women under the age of 50 who were diagnosed with breast cancer between 1996 and 2017, as well as 18,000 women under the age of 50 who were not diagnosed with the disease.
About 44% of those with breast cancer and 39% of the healthy controls had a current or recent hormonal contraceptive prescription, and about half of the birth control was progestogen-only.
Composition of Birth Control Has Little to Do With Breast cancer Risk
The risk of being diagnosed with breast cancer increased by about 25% for women on birth control, regardless of whether it was combined or progestogen-only. This risk was consistent across four types of birth control, which are pills, implants, injections, and IUDs and didn’t change due to factors like age, body mass index, or the number of births.
The researchers also analyzed previous studies that examined breast cancer risk among women taking different types of progestogen-only birth control. That data was consistent with the new data they collected, as well as data from studies on breast cancer risk in people taking combination hormonal birth control. These previous studies did not all take into account the same factors that might influence their results, such as age at first birth, but in general, these factors appeared to have little impact on the results.
The researchers estimated the 15-year ‘excess risk’ of being diagnosed with breast cancer if you’ve used either combination or progestogen-only birth control this estimate covers five years of contraceptive use followed by 10 years off contraceptives. It amounted to about 8 of 100,000 users aged 16 to 20 years old, 61 of 100,000 users aged 25 to 29 years old, and 265 of 100,000 users aged 35 to 39 years old, who have a higher baseline risk of breast cancer than younger people.
Given that combination hormonal birth control has long been used despite this same association, the findings will likely not have a major impact on whether people choose to take progestogen-only birth control, according to the authors.
Birth Control: Double Edged Sword
They also noted 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. This is a well-established benefit of combination contraceptives, but the link is less clear for progestogen-only options.
“That protection against endometrial cancer and ovarian cancer actually persists into middle age,” Gillian Reeves, director of the Cancer Epidemiology Unit at the University of Oxford and co-author of the study, said during the press conference.
The study included a small number of people who had copper IUDs, which do not contain hormones, but the researchers said they didn’t have enough data to determine if this form of birth control is associated with breast cancer risk or not.
- Combined and progestagen-only hormonal contraceptives and breast cancer risk: A UK nested case-control study and meta-analysis – (https:journals.plos.org/plosmedicine/article?id=10.1371/journal.pmed.1004188)