Over the past 30 years, researchers have identified many factors that increase breast cancer risk and a few factors that lower risk. Some of these factors affect risk a great deal and others by only a small amount.
Although we have learned a lot, we still do not understand what causes breast cancer to develop at a certain time in a certain person. It's likely a combination of risk factors (many of which are still unknown). But, why a certain combination of factors might cause cancer in one person, but not in another, is still unclear.
No one has control over whether he/she gets breast cancer. Many risk factors are still unknown and many are simply out of our control (such as getting older or having a family history of breast cancer). However, there are things you can do that may lower your risk, such as leading a healthy lifestyle (more).
And, knowing what factors may increase your risk can help you work with your health care provider to address any concerns you may have and develop a breast cancer screening plan that is right for you. Learn more about breast cancer screening.
Susan G. Komen®’s breast self-awareness messages
1. Know your risk
- Talk to both side of your family to learn about your family health history
- Talk to your health care provider about your personal risk of breast cancer
2. Get screened
3. Know what is normal for you and see your health care provider if you notice any of these breast changes (see images):
- Lump, hard knot or thickening inside the breast or underarm area
- Swelling, warmth, redness or darkening of the breast
- Change in the size or shape of the breast
- Dimpling or puckering of the skin
- Itchy, scaly sore or rash on the nipple
- Pulling in of your nipple or other parts of the breast
- Nipple discharge that starts suddenly
- New pain in one spot that doesn't go away
4. Make healthy lifestyle choices
Learn more about risk and risk factors.
Estimating breast cancer risk
To estimate your risk of breast cancer, health care providers look at:
- How many risk factors you have
- How much these factors increase risk
While a few factors increase breast cancer risk a lot (like a BRCA1 gene mutation), most known factors have only a small or modest effect on risk.
Exactly which risk factors should be used to estimate risk is still under study.
Breast Cancer Risk Assessment Tool (the Gail model)
The Breast Cancer Risk Assessment Tool (the Gail model) is often used by health care providers to estimate risk. This model considers many risk factors and is used for women in the general population. Learn more about the Breast Cancer Risk Assessment Tool or visit the National Cancer Institute website to access the online tool.
Other tools (such as BRCAPRO, the Claus model and the Tyrer-Cuzik model) use family history to estimate breast cancer risk. Such tools can be used for women who have one or more relatives with breast cancer .
Where do the data come from?
The data in this section come from two main types of research studies:
The goal of these studies is to give information that helps support or disprove an idea about a possible link between an exposure (like alcohol use) and an outcome (like breast cancer) in people. Although they have the same goal, observational studies and randomized controlled trials differ in the way they are conducted and in the strength of the conclusions they reach.
Learn more about different types of research studies.
Animal studies add to our understanding of how and why some factors cause cancer in people. However, there are many differences between animals and people that make it hard to translate findings directly from one to the other. Animal studies are also designed differently than human studies. They often look at exposures in larger doses and for shorter durations than are suitable for people. Thus, animal studies can lay the groundwork for research in people, but in order to draw conclusions for people, we need human studies.
All data presented within the Understanding Breast Cancer section of this website come from human studies unless otherwise noted.
Finding information on risk factors for breast cancer
Some organizations conduct research and/or prepare summary reports of research on certain exposures shown to have a link (or no link) to breast and other types of cancer. These agencies are a good place to find detailed, up-to-date information (for example, if you have concerns over a news item on cancer).
IARC is a part of the World Health Organization. The CDC, NTP and FDA are all part of the U.S. Department of Health and Human Services.