Hormonal contraceptives and breast cancer: Weighing up the risks

A recent study by the Oxford Population Health’s Cancer Epidemiology Unit has found that the use of hormonal contraceptives is associated with a 20-30% higher relative risk of breast cancer. This includes the combined oral contraceptive pill (often known simply as ‘the pill’), and the progestogen-only pill (known as ‘POP’, or the ‘mini pill’).

The researchers found that the increased risk was consistent no matter how the hormonal contraceptive was taken – the risk was broadly similar for pills, injections, implants, and hormone-releasing intrauterine devices.

Why was the study done?

We have known that combined oral contraceptives (those containing oestrogens as well as progestogens) are associated with a small increase in breast cancer risk since the 90s, but comparatively little research into the dangers associated with progestogen-only contraceptives has been carried out.

The Oxford study, funded by Cancer Research UK (CRUK), sought to fill the gaps in our understanding of the interplay between hormonal contraception, especially progestogen-only, and breast cancer risks. Considering that from 2010 to 2020 oral progestogen-only contraceptive prescriptions almost doubled, understanding how their use may be linked to breast cancer has become increasingly important.

About the study

The study included 9,498 women under the age of 50 who had been diagnosed with breast cancer and were matched to 18,171 similar women who had not been diagnosed with breast cancer. This allowed the researchers to examine the relationship, if any, between the use of hormonal contraceptives and a higher risk of breast cancer.

The researchers gathered data from prescription histories, meaning there were no issues with participants trying to recall what contraceptives they had taken in the years leading up to their cancer diagnosis. However, complete prescription histories for many of the participants were not available.

This means that although the team were able to draw conclusions about the short-term risks associated with the use of hormonal contraceptives, they couldn’t assess any possible long-term effects. Previous research has shown that ten or more years after ceasing the use of combined oral contraceptives, there was no observed increase in the likelihood of a breast cancer diagnosis.

What do these numbers actually mean?

Although a 20-30% increase sounds like a lot, it’s important to understand this is a relative increase in the possibility of developing breast cancer. According to CRUK, around 14% of females in the UK will be diagnosed with breast cancer in their lifetime. An increase of 30% would raise this number to around 18% of females in the UK – a fairly small increase in actual risk.

Put another way, we can ask how many extra people per 100,000 people would be expected to develop breast cancer in association with oral contraceptives in a 15 year period. For 16 to 20 year olds, the authors estimate that eight extra people per 100,000 would develop breast cancer, whereas for the ages 35-39 they suggest an extra 265 cases per 100,000 people.

The younger age bracket is expected to see fewer extra cases, as the baseline risk of developing breast cancer increases steadily with age.

What about other breast cancer risk factors?

There are many factors that contribute to a person’s risk of developing breast cancer, such as age, family history and genetics, obesity, and individual physiology. There are also various factors that can be controlled, such as alcohol use, tobacco use, and level of exercise.

For example, the risk of developing breast cancer is 28% higher amongst people with the highest levels of lifetime alcohol consumption compared to those with the lowest. In addition, current smokers are up to 13% more likely to develop breast cancer. Women with the lowest levels of physical activity are also 13% more likely to develop breast cancer than those with the highest levels of activity.

So, although hormonal contraceptives are associated with an increased risk of breast cancer, their effect is still fairly minimal compared to other risk factors. To put this into context, in 2015 8% of breast cancer cases in the UK were attributed to obesity or unhealthy weight, whereas only 0.8% of cases were attributed to oral contraceptives. In addition, the small increase in risk observed in this study

Weighing up the options

Whilst it’s important for us to know the risks associated with using hormonal contraception, it’s also important to consider this in the context of the benefits of effective contraception. Equally, non-hormonal alternatives such as the copper coil and vasectomies are just as effective and have not been linked to an increase in breast cancer.

As with most health questions, there is no one-size-fits-all solution, so if you have any questions it’s best to talk to your GP.