There are many things that you can do to help lower your risk for breast cancer. Exercising every day, avoiding alcohol, and maintaining a healthy weight all help decrease the likelihood that you will develop breast cancer.
That information tells you that you should exercise every day, reduce your use of alcohol and achieve or maintain a healthy weight. You could just agree and take those actions. But sometimes you might want to know what will make the biggest difference, or how much difference a particular lifestyle change could make for you. Will giving up your usual after-work bar visit really make so much difference in your risk of breast cancer that it’s worth that big a change? Or maybe you just want to understand the research reports more fully. A headline saying that alcohol increases breast cancer risk by 15% — or 50% — sounds pretty serious. But does that actually mean that your after-work beer makes your chance of getting breast cancer shoot up by 15% or 50%?
One thing to understand is that some of those figures are about relative risk and some are about absolute risk. What’s the difference between relative risk and absolute risk, anyway?
What is relative risk?
Relative risk compares the statistical probability that different groups will develop breast cancer. Both relative risk and absolute risk are expressed in a ratio or percentage.
Here’s an example.
Let’s say that researchers conduct a study to determine how exercise can reduce relative risk for breast cancer. The researchers look at two different groups of 100 women. One group exercises for 30 minutes every day, and the other group does not. Two women develop breast cancer in the group that doesn’t exercise, whereas one woman develops breast cancer in the group that does exercise.
In this example, women who did not exercise were twice as likely to develop breast cancer than women who did exercise. This means that exercise resulted in relative risk reduction of 50%.
What is absolute risk?
Absolute risk for breast cancer is a look at an individual’s risk independent of other groups. It’s your personal risk of developing breast cancer over a certain period of time.
For example, one in eight women develops breast cancer over an 80-year lifespan. This means that the average woman has a one in eight, or 12%, probability of developing breast cancer by the age of 80. A woman’s absolute risk for breast cancer isn’t always 12%, however. Other factors – such as your age, family history, or reproductive history – influence your absolute risk.
Let’s look at the above example again. In the example, 2% of the women who did not exercise developed breast cancer, whereas 1% of the women who did exercise developed breast cancer. This means that exercising 30 minutes a day resulted in a 1% decrease in absolute risk for those women.
Your lifestyle choices can affect your risk of developing breast cancer, but making sense of risk factors is easier when you know whether an absolute or relative risk is involved.
Recognizing the difference between absolute risk and relative risk can help you better understand risk reduction and prepare for breast cancer treatment and prevention. Contact The Breast Center in Northwest Arkansas for more information about absolute risk and relative risk for breast cancer.