The table below lists the known risk factors for breast cancer and their relative risks.
A relative risk shows how much higher, how much lower or whether there is no difference in risk in people with a certain risk factor compared to the risk in people without the factor. A relative risk greater than one indicates an increased risk among people with the risk factor compared to people without the factor. A relative risk below one indicates a decreased risk among people with the factor. And, a relative risk of one means there is no difference in risk between people with and without the risk factor.
For example, a relative risk of 1.20 means someone with the factor has a 20 percent higher risk of breast cancer than someone without the factor. A relative risk of 2.0 means someone with the factor has twice the risk (or 2-fold the risk) of someone without the factor. And, a relative risk of 0.80 means someone with the factor has a 20 percent lower risk of breast cancer than someone without the factor.
The impact of a relative risk depends on the underlying absolute risk of the disease. For example, the rate of breast cancer increases with age (see below), and this impacts the number of extra breast cancer cases linked to a risk factor. When a disease is rare, as breast cancer is among very young women, even a high relative risk means that only a few extra cases will occur. By contrast, when a disease is more common, as breast cancer is among older women, even a small relative risk can result in many more cases.
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 1,681 (0.06%)
1 in 232 (0.4%)
1 in 69 (1.4%)
1 in 42 (2.4%)
1 in 29 (3.4%)
1 in 27 (3.7%)
1 in 8 (12.4%)
Source: American Cancer Society, Breast Cancer Facts & Figures 2011-2012 and Cancer Facts & Figures 2013 [4,6].
Factors that Increase the Risk of Breast Cancer
Approximate Relative Risk
Table note: Adding relative risks does not give a total risk score.
Learn about estimating breast cancer risk.
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Breast Cancer Risk FactorsTable
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