Birth Control Breast Cancer Risk Increases Longer Drugs Used: Study

A new study highlights the potential risk of breast cancer from birth control pills, indicating that the risk women face increases the longer they continue to take the oral contraceptives. 

Researchers from the University of Copenhagen published a study on December 7, in The New England Journal of Medicine, which finds that birth control pill may increase the risk of breast cancer by as much as 38%.

The study also indicates that the risk increases with long term use, which is known as a dose-response relationship, providing stronger evidence that the hormonal contraceptives are the cause of the breast cancer cases.

Researchers looked at data on 1.8 million women in Denmark between the ages of 15 and 49 who did not have cancer, blood clot problems, and had not undergone infertility treatments. They looked for hormonal contraception use and breast cancer diagnoses.

According to the findings, at least 11,517 cases of breast cancer were identified from that group. When they looked at the overall risk of breast cancer, researchers found that women who currently or recently used hormonal birth control had a 20% increased risk. However, they also found that women who had been taking birth control pills for less than a year had only a 9% increased risk, but after more than 10 years of use that increased to a 38% higher risk than women who had not taken birth control pills at all.

Even after the women stopped taking the pill, the increased risk remained for five years or more.

Researchers determined that the overall increased risk of breast cancer from taking birth control pills would result in one additional breast cancer case for every 7,690 women who took oral contraceptives for at least one year.

“The risk of breast cancer was higher among women who currently or recently used contemporary hormonal contraceptives than among women who had never used hormonal contraceptives, and this risk increased with longer durations of use; however, absolute increases in risk were small,” the researchers concluded.

The findings are similar to those of a study published in 2014, when Seattle researchers found that women taking high-dose estrogen pills were about 50% more likely to be diagnosed with breast cancer compared to women taking other typs of birth control pills. That study found that newer oral contraceptives were associated with an increased risk, due to the use of progestin ethynodiol diacetate, as well as among women taking pills with triphasic dosing.

According to the American Cancer Society, less than one percent of women under the age of 40 will be diagnosed with breast cancer, and the increased risks indicated by the study would not raise that number considerably.