Taking progestogen-only birth control pills comes with a slightly increased risk of breast cancer -- about the same degree of risk associated with taking pills that contain both progestogen and estrogen, new research finds.
After five years' use, investigators found a 20% to 30% heightened breast cancer risk with both types of contraceptives, according to the study published March 21 in PLOS Medicine.
“These findings suggest that current or recent use of all types of progestogen-only contraceptives is associated with a slight increase in breast cancer risk, similar to that associated with use of combined oral contraceptives,” said study co-author Kirstin Pirie, a researcher at the University of Oxford in the United Kingdom.
Use of progestogen-only contraceptives has increased significantly in recent years, the authors noted.
“Given that the underlying risk of breast cancer increases with advancing age, the absolute excess risk associated with use of either type of oral contraceptive will be smaller in women who use it at younger rather than at older ages,” the authors added in a journal news release.
“These excess risks must, however, be viewed in the context of the well-established benefits of contraceptive use in women's reproductive years,” they continued.
For the study, researchers analyzed nearly 10,000 women with breast cancer under the age of 50. Researchers also included data on more than 18,000 closely matched controls.
Data came from a U.K. primary care database. The women had been diagnosed with breast cancer between 1996 and 2017.
About 44% of women with breast cancer and 39% of matched controls had a hormonal contraceptive prescription. About half the prescriptions were for progestogen-only medications.
The associated 15-year absolute excess incidence of breast cancer was estimated at 8 cases per 100,000 hormonal contraceptive users at age 16 to 20 after five years' use. It was 265 cases per 100,000 users for those ages 35 to 39.
The relative increase in risk of breast cancer was 23% in those with combined oral pills; 26% in those with progestogen-only pills; 25% in those with injected progestogen, and 32% with an intrauterine device releasing progestogen.
These results were combined with those from previous studies from high-income countries, which included women from a wider age range.
The U.S. Centers for Disease Control and Prevention has more on breast cancer.
SOURCE: PLOS Medicine, news release, March 21, 2023