Originally published on the Susan G. Komen site
There’s been great progress over the last 30 years in identifying risk factors for breast cancer. At this time, researchers agree on many factors that increase breast cancer risk and several factors that lower risk. Some of these risk factors affect risk a great deal and others by only a small amount.
While there have been great advances in our knowledge, it’s still not understood 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) that together make cells in the breast turn cancerous. But exactly why a certain combination of factors might cause cancer in one person, but not in another is still unclear.
Although there are steps nearly everyone can take to lower risk, no one has full 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 is a lot that you can do to reduce your risk from breast cancer. Leading a healthy lifestyle can help lower risk and getting regular screening tests can find breast cancer early, when it’s most treatable. Finally, knowing what factors may increase your risk can help you work with your health care provider to address any concerns and develop a breast health plan.
For more information on risk and risk factors, visit Understanding Risk.
Estimating breast cancer risk
In general, your risk of breast cancer is estimated by how many risk factors you have and by how much these factors increase risk. While there are a few factors that greatly increase breast cancer risk (like a BRCA1 gene mutation), most known factors have a small or modest effect on risk. Exactly which of these risk factors should be considered when estimating risk is still an active area of study.
The Gail model is a tool often used for estimating a woman’s risk of breast cancer. This model considers a large number of risk factors and is used for women in the general population. One drawback to this model is that it may underestimate risk in certain groups of women. For more on the Gail model and a link to the online tool based on it, click here. Other tools, such as the Claus model, use family history to estimate breast cancer risk. These tools can be used for women who have at least one relative with breast cancer.
Where do the data come from?
The data in this chapter come from two main types of research studies: observational studies (prospective cohort or case-control) and randomized controlled trials. The goal of these studies is to give information that helps support or disprove an idea about the 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. For more on research studies, visit the Breast Cancer Research section.
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 and often look at exposures in larger doses and for shorter durations than are suitable for humans. Thus, animal studies can lay the groundwork for human research, but in order to draw conclusions for human populations, we need human studies. All data presented on this website come from human studies unless otherwise noted.
Several organizations conduct research and/or prepare summary reports of research on certain exposures that have been linked to breast and other types of cancer. If you have concerns over a news item on cancer for example, these agencies are a good place to find detailed, up-to-date information. The International Agency for Research on Cancer (IARC) is a part of the World Health Organization. The National Toxicology Program is part of the U.S. Department of Health and Human Services and the U.S. Food and Drug Administration (FDA) and the Centers for Disease Control and Prevention (CDC) are also federal agencies.