10 December 2017

A study published in the New England Journal of Medicine has shown that birth control pills and other forms of hormone based contraception (such as some intrauterine devices (IUDs) are associated with an increased risk of breast cancer. We’ve thought that the pills currently in use, which have much lower doses of estrogen and progesterone compared to older formulations, did not have a significant impact on breast cancer risk. However, the study showed a small but increased rate of breast cancer developing in those using birth control pills and IUDs.

The large study (1.8 million women), performed in Denmark, evaluated the breast cancer risk in women under the age of 50. The breast cancer risk associated with hormonal birth control is small – out of 100,000 women, there was an increase of 13 breast cancers per year (68 / year in the hormonal contraception group and 55 per year in the non-users). Most of the cases that occurred in this study were in women in their 40s. In women under the age of 35, the increased risk was 2 cases per 100,000 women.  As limitation of the study is that it did not take into account other breast cancer risk factors such as breast feeding history, alcohol intake, and exercise patterns. Breast cancer risk increased with duration of contraceptive therapy. It is important to note that as this was an observational study, it cannot conclusively be stated that hormonal contraception causes breast cancer – only that it is associated with an increased risk.

The increased risk needs to be balanced against the potential benefits of hormonal contraceptive therapy, such as preventing unwanted pregnancy, control of heavy bleeding especially during the perimenopausal period, and reduction in the subsequent risk of ovarian, endometrial and (possibly) colorectal cancers. Potential risks of long term hormonal contraception include an increased incidence in blood clots (especially in women who are overweight and/or smokers) and stroke.

Patients should evaluate their risk tolerance, breast cancer risk factors, and the risks and benefits of hormonal contraception in their individual case. As expected, the media coverage on the story is variable – HealthNewsReview.org did a good job of evaluating the media coverage and summarizing the important points of the study.

Additional Information:
NEJM Editorial
NPR – Even Low Dose Contraceptives Slightly Increase Breast Cancer Risk 
NY Times – Birth Control Pills Still Linked to Breast Cancer Risk
NY Times – Birth Control and Breast Cancer – Putting the Risk into Perspective