Hormonal birth control linked to increased risk of breast cancer

by Jacob Fuller

Lauren Dempsey, MS in Biomedicine and Law, RN, FISM News 

Hormonal birth control can increase women’s risk of breast cancer, according to a new study by researchers at the University of Oxford.

The study, which was published in PLOS Medicine last month, evaluated data from thousands of women under the age of 50 that had been diagnosed with invasive breast cancer.

Hormonal birth control has been known to carry this risk, however, the team of researchers at Oxford wanted to evaluate the effect of progestagen-only contraceptives on breast cancer risk. Use of progestagen-only hormonal contraceptives has steadily increased, almost equaling the number of prescriptions for combined oral contraceptives in England.

The researchers analyzed data from 9,498 women who were diagnosed with invasive breast cancer between 1996 and 2017 in the U.K. Researchers also collected data from 18,171 women who did not have breast cancer. Women involved in the study were between 20 and 49 years old with 2% aged below 30 years, 21% aged 30 to 39 years, and 77% aged 40 to 49 years.


The results show that 44% of women with breast cancer had hormonal birth control prescriptions and 39% of the women in the control group had a prescription for hormonal birth control; with about half having prescriptions for progestin-only in both groups. The study also found that the estimated 15-year absolute excess risk associated with 5 years of hormonal contraceptive use was 8 per 100,000 women ages 16 to 20 and 265 per 100,000 women ages 35 to 39.

While the findings suggest that there is a relative increase of 20% to 30% in breast cancer risk associated with current or recent use of either combined oral or progestagen-only contraceptives, the risk is still relatively low.

The researchers were able to gather data on the short-term association between hormonal birth control and an increased risk for breast cancer. However, they were not able to provide new data on long-term associations between the two. There were also numerous limitations, including previous prescription history and family history of breast cancer.

The researchers noted,

it is unclear what effect, if any, adjustment for family history of breast cancer would have made to our findings, previously published findings for combined oral contraceptives were unaltered after adjustment for family history, and two studies of progestagen-only contraceptives included in our meta-analysis found little change in associated risks after adjustment for a number of additional factors including family history.

However, while the team acknowledged these limitations, they do not believe that it had an impact on the results or their ability to analyze short-term associations.

The National Cancer Institute explains that birth control contains hormones estrogen and progesterone and that the synthetic versions of these hormones may increase the risk of cancer by stimulating the growth of certain cancers as well as changing the susceptibility of cervical cells to HPV and therefore increasing the risk of cervical cancer.

Hormonal birth control has also been linked to an increased risk for stroke, hair loss, high blood pressure, weight gain, pulmonary embolisms, anaphylaxis, ectopic pregnancy, depression, anxiety, and suicidal ideations. It is also contraindicated for women who smoke, are over the age of 35, have a history of high blood pressure, diabetes, or history of stroke, heart attack, or blood clots in the legs or lungs.