The table below shows the relative risk of breast cancer linked to a variety of factors. The relative risk represents how much higher or lower the risk of breast cancer is for a person who has the factor compared to a person who does not.
Factors are grouped based on the strength of the scientific evidence for each risk.
- Established and probable have the strongest evidence behind them and are recognized as linked (or not linked in some cases) to breast cancer.
- Possible factors have less evidence behind them; they suggest links to breast cancer but need more study before solid conclusions can be made.
- Insufficient or inconsistent factors are backed by few studies or the studies to date have very mixed results, which don't allow comment on any potential link with breast cancer.
Click on any of the factors to learn more.
Relative Risk CategoriesWhere do the data come from?
The data in this table 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 Web site 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.
Updated 11/16/09
