There are lots of risk factors linked to breast cancer. The two most common, being a woman and getting older, are beyond your control. But some things, like exercising, maintaining a healthy weight and limiting your alcohol intake, are within your power. In this section, you’ll get a better understanding of risk, the factors that affect it, how to assess yours and how to manage it. Knowing these things can help you make decisions about your lifestyle and, working with your health care provider, determine a breast cancer screening plan that’s right for you.
Over the past 30 years, researchers have identified many factors that increase breast cancer risk and a few factors that lower it. Some factors affect risk a great deal and others by only a small amount.
We’ve learned a lot but we still don’t understand what causes breast cancer to develop at a certain time in a certain person. It's likely a combination of factors. And although there are things you can do to manage your risk, no one has control over whether he or she gets breast cancer.
Every day, we take steps to reduce the risks in our lives. We wear seat belts to reduce the chance we’ll get hurt in a car accident. We brush our teeth to prevent cavities. And while most of us don't spend too much time thinking about risk, it's important to understand the concept of risk as it relates to health.
"Risk" in the health and medical fields can have special meanings. Knowing the basic types of risk can help you understand your chances of getting breast cancer and the steps you can take to lower your risk.
The most basic type of risk is absolute risk, a person's chance of developing a certain disease over a certain period of time. Absolute risk is estimated by looking at a large group of similar people and counting how many develop a certain disease over a certain period of time. Knowing the absolute risk of a disease can help you understand the health risks in your life.
The examples below show that the absolute risk of breast cancer is low in young women and much higher in older women.
If we followed 100,000 women ages 30 to 34 for one year, about 25 women would develop breast cancer . This means the one-year absolute risk of breast cancer for a 30- to 34-year-old woman is 25 per 100,000 women (or 1 per 4,000 women) or a risk of less than 1 percent.
From the examples above, we see that the absolute one-year risk of breast cancer for a woman is low. But you may see absolute risk presented over longer periods of time. The table below shows the 10-year absolute risks of breast cancer by age.
Absolute risk of breast cancer in American women by age
If current age is:
Absolute risk of developing breast cancer in the next 10 years is:
1 in 1,732 (0.06%)
1 in 228 (0.4%)
1 in 69 (1.5%)
1 in 43 (2.3%)
1 in 29 (3.5%)
1 in 26 (3.8%)
1 in 8 (12.3%)
Source: American Cancer Society [4,515].
Say a study shows that women who don't exercise (inactive women) have a 25 percent increase in breast cancer risk compared to women who do exercise (active women). This statistic is a relative risk (the relative risk is 1.25). It means inactive women are 25 percent more likely to develop breast cancer than women who exercise.
The impact of a relative risk depends on the underlying absolute risk of a disease.
We can think about relative risk in terms of money. If you have a single dollar, this makes dollars "rare.” If you double your money, you only gain one extra dollar. But, if you have a million dollars, this makes dollars "common" and a doubling your money means you gain a million extra dollars. In both cases, you double your money, but the real increase in dollars is quite different. The same is true with disease risk. The higher the absolute risk of getting a disease, the greater the number of extra cases that will occur for a given relative risk.
Using our example of the exercise study, we can also show how absolute risks affect the number of extra cases. Inactive women have a 25 percent greater risk of breast cancer than active women (a relative risk of 1.25). Since older women are more likely to get breast cancer, lack of exercise has a greater impact on breast cancer risk in older women than in younger women.
Let’s first look at the women in the study ages 70 to 74 years. The study finds that 500 women per 100,000 who are inactive develop breast cancer during one year (this is the absolute risk for women with the risk factor, lack of exercise). The study also shows that 400 women per 100,000 who are active develop breast cancer (this is the absolute risk for women without the risk factor).
So, the relative risk is 1.25 for women who are inactive compared to those who are active.
Among women ages 70 to 74, being inactive led to 100 more cases of breast cancer per 100,000 women in one year (500 cases – 400 cases = 100 cases).
Now let’s look at the women in the study ages 20 to 29. The study finds that 5 per 100,000 who were inactive developed breast cancer in the next year. And, 4 women per 100,000 who were active got breast cancer.
Here, the relative risk is also 1.25. However, in women ages 20 to 29, being inactive led to only one extra case of breast cancer per 100,000 women (5 cases – 4 cases = 1 case).
So, the same relative risk of 1.25 led to many more extra cases of breast cancer in the older women (100 extra cases) than in the younger women (one extra case). The impact of the same relative risk (1.25) was different depending on the underlying absolute risk.
Relative risks can be presented in many ways. This guide may help you recognize a relative risk when you see or hear it.
When a relative risk is between 1 and 1.99 it may be presented in several ways. For example, in the exercise study above, the relative risk is 1.25. You may see:
When a relative risk is 2 or more, it is often presented as how many times the risk is increased. For example, women with atypical hyperplasia, a benign breast condition, have a relative risk of about 4 compared to women without atypical hyperplasia. You may see:
When a relative risk is less than 1, it means that the risk factor lowers the risk of disease. For example, women who breastfeed (for a lifetime total of one year or more) have a relative risk of breast cancer of about 0.75 compared to women who do not breastfeed. You may see:
You can put your understanding of relative risks to work right away. Our Breast Cancer Research section has summary tables of the current body of research on the topics ranging from risk factors to treatment to social support. These tables show some of the research behind many of the recommendations and standards of practice discussed throughoutthe About Breast Cancer section.
If you’re not familiar with how the research process works (or just need a refresher), “How to read a research table” is a good place to start before looking at the tables.
Learn more about breast cancer research.
Understanding absolute risk and relative risk can help you be a well-informed consumer of health information. You can also use this knowledge to make informed choices about your health.
No matter what your underlying risk of breast cancer is, a healthy lifestyle is always important. Learn more about healthy behaviors and breast cancer risk.
The Breast Cancer Risk Assessment Tool (the Gail model) was designed by researchers at the National Cancer Institute and the National Surgical Adjuvant Breast and Bowel Project as a tool for health care providers. The tool calculates a woman's risk of developing breast cancer within the next five years and within her lifetime (up to age 90). It takes into account seven key risk factors for breast cancer.
Women with a five-year risk of 1.67 percent or higher are classified as "high-risk." This score (a five-year risk of 1.67 percent or higher) is the cutoff for the FDA guidelines for taking tamoxifen or raloxifene to reduce breast cancer risk.
Learn more about risk-lowering drugs.
The Breast Cancer Risk Assessment Tool cannot predict whether or not you will develop breast cancer. It does not calculate an individual woman’s breast cancer risk, but rather the average risk for a group of women with similar risk factors. So, it is not clear what this risk means for any one woman.
Say the tool gives you a five-year risk of 1.7 percent. This means the tool estimates that 1.7 percent of women who have risk factors similar to yours will develop breast cancer over the next five years. But, the tool cannot predict which of these women will go on to be diagnosed.
The Breast Cancer Risk Assessment Tool was designed to be used by health care providers. So, if you use the tool on your own, it may be hard to understand what the risk it calculates means for you. If you have questions about your risk of breast cancer, talk to your provider.
The Breast Cancer Risk Assessment Tool does not give a good estimate of risk in some women including those with :
The original model was based on data from white women. Recently, the model was updated to estimate risk for:
It's still not clear how well the model works in other racial/ethnic populations.
The Breast Cancer Risk Assessment Tool also does not use all the known (established) risk factors for breast cancer to assess risk.
Even with its current limitations, the Breast Cancer Risk Assessment Tool can be useful. However, it is not a perfect predictor of individual risk. The model can estimate your risk, but it cannot tell whether or not you will get breast cancer.
Visit the National Cancer Institute website to access the Breast Cancer Risk Assessment Tool.
As research in risk assessment grows, tools like the Breast Cancer Risk Assessment Tool will become better able to predict risk in large groups of women.
Learn about new methods of estimating risk.
Every day, we take steps to prevent unwanted events from happening. For example, we brush our teeth to prevent cavities. We would like to ensure some events never happen, but the best we can do is lower our risk. We know people who brush their teeth can still get cavities.
We do what we can to improve the chances of a good outcome, but we don't always have complete control. The same concept applies to cancer and other chronic diseases. In the public health setting, the term “prevention” mainly refers to lowering the risk of getting a disease rather than completely removing the risk. You may also hear the term “risk reduction.”
Cancer tends to be caused by a combination of factors. Some factors we may be able to control (like exercise), some are out of our control (like age) and some are still unknown.
Since many factors drive cancer risk and we can control only some of these, we cannot avoid some amount of risk. For example, the two most common risk factors for breast cancer, being a woman and getting older, are not things you can control.
For breast cancer, most risk factors that we have some control over have only a small effect on risk. This means there is no one behavior that will prevent breast cancer. But, it also means there's no one factor that will cause it. Even a woman with a BRCA1 or BRCA2 gene mutation doesn't have a 100 percent chance of getting breast cancer. In fact, most people diagnosed with breast cancer are at average risk and we don’t know which factors came together to cause the cancer.
Because the disease process is so complex, it's hard to pin down how a certain set of risk factors will affect a person. When we look at groups of people it becomes clearer. For example, if we find there is a 20 percent decrease in risk of breast cancer in one group of people, we can predict there will be a 20 percent decrease in risk in a similar group. What we don't know is which specific people in the group will get the prevention benefit.
It’s hard to know who benefits from prevention. We know some behaviors can lower the risk of cancer, but we don’t know how great the benefit is for any one person. For example, non-smokers are much less likely to develop lung cancer compared to smokers. However, we do not know who prevents lung cancer by not smoking and who would have remained cancer-free even if they had smoked. Further, most smokers will never be diagnosed with lung cancer and some non-smokers will. So, taking steps to prevent cancer lowers risk, but it does not ensure a person never develops the disease.
The good news is there are some healthy behaviors that are under our control that may reduce the risk of breast cancer. And, making healthy choices can lower the risk of other types of cancer as well as many other chronic diseases such as diabetes and heart disease.
Learn more about healthy behaviors and breast cancer risk.
Factors inside and outside our bodies affect our health. Those outside our bodies are often called environmental factors. There is no one scientific definition for the term “environment.” In health research, different scientists may use different categories when deciding whether a risk is environmental.
Environmental factors may include things found in nature that we eat, drink, touch or breathe, as well as man-made factors. Possible examples include exposures that are passive (such as sunlight or secondhand smoke) and those that are active (such as eating fruits and vegetables or drinking alcohol). Even medications, such as birth control pills or menopausal hormone therapy (postmenopausal hormones), are sometimes considered environmental exposures.
Factors such as age, the hormones produced in our bodies (such as estrogen) and family history are considered to be personal or genetic factors rather than environmental factors. However, they can interact with environmental factors and affect our health.
Some factors in our environment help keep us healthy. Others can increase our risk of breast cancer or other diseases. Still others have little, if any, effect on our health.
Researchers can use different types of studies to learn about the environment and breast cancer risk.
Facts for Life: Breast Cancer Risk Factors
Breast Cancer 101 - Risk Factors
How to assess your breast cancer risk factors?