Breast Cancer Risk

The term “risk” is used to refer to a number or percentage that describes how likely a certain event is to occur. When we talk about factors that can increase or decrease the risk of developing breast cancer, either for the first time or as a recurrence, we often talk about two different types of risk: absolute risk and relative risk.

Absolute risk
Absolute risk is used to describe an individual’s likelihood of developing breast cancer. It is based on the number of people who will develop breast cancer within a certain time period. Absolute risk also can be stated as a percentage.

When we say that 1 in 8 women in India, or 13%, will develop breast cancer over the course of a lifetime, we are talking about absolute risk. On average, an individual woman has a 1-in-8 chance of developing breast cancer over an 80-year lifespan.

The absolute risk of developing breast cancer during a particular decade of life is lower than 1 in 8. The younger you are, the lower the risk. For example:

From age 30 to 39, absolute risk is 1 in 233, or 0.43%. This means that 1 in 233 women in this age group can expect to develop breast cancer. Put another way, your odds of developing breast cancer if you are in this age range are 1 in 233.
From age 40 to 49, absolute risk is 1 in 69, or 1.4%.
From age 50 to 59, absolute risk is 1 in 38, or 2.6%.
From age 60 to 69, absolute risk is 1 in 27, or 3.7%.
As you can see, the older you are, the higher your absolute risk of breast cancer. Keep in mind that these numbers and percentages are averages for the whole population. Your individual breast cancer risk may be higher or lower, depending on a number of factors, including family history, reproductive history (such as menstrual and childbearing history), race/ethnicity, and other factors.

Take family history, for example. The absolute risk of breast cancer is much higher for women who have inherited mutations in the genes known as BRCA1 or BRCA2. Their absolute risk over the course of a lifetime ranges from 40-85%. This means that out of every 100 women who have these mutations, anywhere from 40 to 85 of them can expect to develop breast cancer should they live to age 80.

If you have breast cancer, absolute risk also can be used to describe the likelihood of a certain treatment outcome or the course of the disease. For example, suppose that, based on the characteristics of the breast cancer (stage, grade, other test results), your age and medical history, and the treatments you have, your doctor tells you that your likelihood of disease-free survival at 5 years — being alive with no evidence of breast cancer — is 90%. This means that your absolute risk of having the breast cancer come back within 5 years is 10%, or 1 in 10. In other words, 1 out of 10 women with similar characteristics and the same treatment plan can expect to have a recurrence within that time frame. Nine out of 10, or 90%, would not.

Relative risk
Relative risk is a number or percentage that compares one group’s risk of developing breast cancer to another’s. This is the type of risk frequently reported by research studies, which often compare groups of women with different characteristics or behaviors to determine whether one group has a higher or lower risk of breast cancer than the other (either as a first-time diagnosis or recurrence).

Understanding relative risk can help you answer an important question: If I make certain lifestyle choices or have certain treatments, how much will I increase or decrease my risk of developing breast cancer or having a recurrence?