Causes of Breast Cancer

An understanding of the factors that cause breast cancer may allow you to lower your risk and help prevent the disease step by step.

There are different ways of looking at breast cancer risk. For more information see both the three levels of risk and the short video below.

Lifetime Risk

Lifetime risk is the chance that you will get breast cancer at any time during your entire life. In the UK and northern Europe the risk is sometimes referred to as a 1 in 8 lifetime risk. However this figure includes women diagnosed with DCIS (pre-invasive cancer that may never progress to invasive cancer) and women over 85 years of age (when breast cancer may not alter life expectancy), and so at Prevent Breast Cancer we prefer to use the figure 1 in 9 lifetime risk as a more realistic reflection of UK risk.

Relative risk

In the following section on risk factors, risk is often referred to as relative risk. This means that the extra ‘relative risk’ needs to be calculated relative to the background risk that the individual concerned starts off with. For example, the extra 20% risk of breast cancer caused by the contraceptive pill sounds alarming at first glance. However, if you are 25 years of age your background risk of developing breast cancer at all is extremely small; perhaps around a 0.1% chance over the next 10 years. The extra risk from the pill only increases the risk by 20% of 0.1% which is 0.02% extra (or put another way, a 1 chance in 5,000). This is such a tiny extra risk that it may not influence your life decisions.

Absolute risk

Another way of expressing risk is your absolute risk over a period of time. For example, if you are 30 years of age your absolute risk of breast cancer is typically around a 2% chance between the ages of 30 and 50. Or, if you are 50 years of age your risk will be 5% between the ages of 50 and 70.

The single most important factor that increases your absolute risk is a strong family history. Thus, if a close family member had breast cancer at a young age, your own risk might double from 2% to 4% between 30 and 50 years of age and this would entitle you to early mammography screening from 40. Thus, something else that increased your relative risk by 20% has a bigger effect if you have a higher background absolute risk. If your absolute risk is higher than average, then it may become even more important to lower the risk factors in your life that influence relative risk. Armed with this information we hope that the relative risks described in this section will make more sense!

In the future, we hope that dramatic reductions in risk can be achieved – and thus the vision of Prevent Breast Cancer is to make 1 in 9 women who develop breast cancer, none in nine.

To find out how specific factors could increase the risk of breast cancer please click here