Types of Risk

There are many different ways to express a woman's breast cancer risk. It can be calculated for a lifetime, or for a specific period of time; in absolute terms or relative to other women. There are several special terms related to these measurements, so it's important to define and understand the language that physicians use in talking about risk.

There are three main measurements of risk:

1. Absolute risk
2. Relative risk
3. Attributable risk

Absolute risk
Absolute risk is the percent chance that a woman will develop breast cancer during a certain period of time (5 years, 10 years, 20 years, etc.). If the time period examined is a lifetime, we use the term "cumulative risk."

Cumulative risk describes a woman's chance of getting breast cancer over her entire lifetime. It is the source of the familiar "1 in 8 women will get breast cancer in their lifetime" statistic for non-Hispanic, Caucasian women. Cumulative risk describes the average risk of breast cancer for a population of women – the estimate is not based on each individual woman's profile. As a result, this number will overestimate risk for women with no known risk factors and underestimate risk for those with identified risk factors.

Relative risk
Relative risk is a comparative measurement. It compares the breast cancer risk of women with particular risk factors to women who do not share the same risk factors. Many of the breast cancer statistics we read in the news are expressed in terms of relative risk. Here's an example:

"Having two biopsies before the age of 50 increases a woman's relative risk of breast cancer by 3 times."

A woman who has had 2 biopsies before the age of 50 is 3 times more likely to develop breast cancer compared to a woman who has not had 2 biopsies before the age of 50.

Always consider the baseline risk of the group used as a comparison. In this example, we are comparing women who have had 2 biopsies before they reach 50 years of age to women who have not had 2 biopsies by age 50.

As an example, assume that the women without biopsies had a 1% chance of developing breast cancer in the next 5 years. For the women who had had 2 biopsies, you would multiply 1% by 3 times. Their risk is still only 3% in this hypothetical example. That's why it is important to remember that relative risk is all relative to the group used as a comparison.

You may see relative risk expressed as a ratio (ex: 1.5). This number 1.5 means that a woman with a particular risk factor is 1.5 times more likely to develop breast cancer than someone without that risk factor.

Another way to express this number is to say that the risk factor increases relative risk by 50%. However, it's important to ask... "50% increase relative to what?" If the baseline risk level we're comparing to is 1%, a 50% increase isn't as meaningful.

Attributable risk
This term pertains to risk within a large population of people, not to the risk level of an individual woman. Attributable risk is calculated by determining how commonly a particular risk factor (like family history) is found in the population, and the relative risk associated with that factor. Sample sentence:

"Risk Factor A has an attributable risk of 9%."

Risk Factor A explains 9% of the breast cancers found in the population.

As you probably have concluded by now, assessing your breast cancer risk thoroughly requires more than just one technique. If you are interested in better understanding your risk, the best way to start is by talking with your doctor about the methods described in this section, and/or asking for a recommendation of a nearby center that specializes in breast cancer risk assessment.