For decades, researchers have looked at how hormonal birth control affects the risk of developing breast cancer. Studies show that using birth control that contains estrogen and progesterone increases your risk of developing breast cancer.
The use of the different types of hormonal contraceptives has changed over the last 10 years. More women are now using progesterone-only preparations, both as oral (eg “mini pill”) and as long-acting formulations such as injectables, implants, and progesterone-releasing coils, or intrauterine devices (IUDs).
New research shows the risk of developing breast cancer is increased further by using progestogen-only contraceptives. A recent study published in PLOS Medicine looked at almost 30,000 women who received a diagnosis of invasive breast cancer between 1996 and 2017. Study participants were compared to evaluate if women who took progesterone-only contraception had a higher risk of developing the disease. The study found that women who used progesterone-only contraception had a slightly increased chance of developing breast cancer. This risk was 20-30% higher than women who took combined (estrogen and progesterone) hormonal contraception.
The actual risk of getting breast cancer when you are young is very small. When you are 20, your risk of getting breast cancer is less than 1 in 1000. When you are 40, your risk increases to 1 in 65 women. The risk increases further with increasing age. This is because as we get older, cells in our body are more likely to mutate as they divide. This Higher rate of “faulty” cell division is a normal consequence of aging. A woman’s overall lifetime risk for developing breast cancer is about 1 in 8. Women and men who are born with certain types of gene mutations (eg in the BRCA gene) are at increased risk of developing breast cancer (and other cancers) compared to people who do not carry those gene mutations.
So, should you stop using your progesterone-only pill, implant, or IUD? This is an important study but it sounds scary and we need to put it in perspective. A 20-30% increase in relative risk may sound like about 1 in 4 women who use this type of contraception will ultimately get breast cancer. That is NOT what these results actually mean.
In reality, the relative increase in breast cancer risk means that if you use progesterone-only contraception for 5 years, the risk of getting breast cancer increases from about 8 in 100,000 between the ages of 16 and 20 years, to about 265 in 100,000 between the ages of 35 to 39 years.
While the results of this study are important to know, they must be viewed in the context of the well-established benefits of contraceptive use during a woman’s reproductive years. Women shouldn’t make a decision about whether to use hormonal contraception or what type specifically, based on this study alone.
Please consult with your doctor to further discuss the pros and cons of the different types of hormonal contraception available, and to help you make the best decision for you.