Risk and Statistics There are three kinds of risk commonly referred to in discussing breast cancer: absolute risk, relative risk, and attributable risk.
Absolute Risk Absolute risk is the rate at which cancer or mortality from cancer occurs in a general population. It can be expressed either as the number of cases per a specified population (e.g., 50 cases per 100,000 annually) or as a cumulative risk up to a particular age. This cumulative risk is the source of the familiar 1 in 8 for non-Hispanic white women.
Your absolute risk also depends to a great extent on your age.
Table 9-2 Age Specific Probabilities of Developing Breast Cancer
If current age is:
The probability of developing breast cancer in the next 10 years is:
Or 1 in:
20
0.05%
1,985
30
0.44%
229
40
1.46%
68
50
2.73%
37
60
3.82%
26
70
4.14%
24
Lifetime Risk
13.22%
8
Source: American Cancer Society Surveillance Research 2005
Relative Risk Relative risk is the comparison of the incidence of breast cancer or deaths from breast cancer among people with a particular risk factor to that of people without that factor, or a "reference population." This type of measurement allows an individual woman to calculate how her individual risk factors will affect her chances of getting breast cancer.
For comparison, you can't use the 1 in 8, or 12 percent, generated in the absolute risk equation, because that is based on all women regardless of risk factors. Instead, you must use the number for women who have no clear risk factors at all. This is 1 in 30, or 3.3 percent, which is significantly lower than the "average" risk of 12 percent.
If you call the risk of the woman without any particular risk factors 1.0, you can report the risk of those with a particular risk factor in relation to this. This is how relative risk is derived. A woman whose mother had breast cancer in both breasts before the age of 40, for example, has a relative risk of 2.7 over her lifetime—that is, 2.7 times that of the woman with no family history, not 2.7 times 12 percent, which is the average risk.
Attributable Risk Attributable risk relates more to public policy. It looks at the amount of disease in the population that could be prevented by alteration of risk factors. Dr. Anthony B. Miller has hypothesized that if every woman in the world were to have a baby before 25, 17 percent of the world's breast cancer would be eliminated if you were looking at this from a public health policy perspective, you'd have to weigh the possible advantages of pushing early pregnancy against the problems of young and possibly immature parents, and possible increased population growth.
The Gail Model for Assessing Risk The Gail Model is one of the models that have been developed to quantify a woman's risk of developing breast cancer. The model incorporates a series of questions related to breast cancer risk factors. Answers to the questions are calculated into a Gail risk score. A woman's risk is considered high if she scores above 1.66 percent. (All women who are over 60 have a score of at least 1.66 and are considered high risk, based on the Gail Model. Women younger than 60 have to have the score of a 60-year-old woman [1.66] to be considered high risk.) Women who score high on the test are encouraged to have increased surveillance and to consider breast cancer risk-reduction options.
The Gail Model is often used in research studies to evaluate which women are at high risk for developing breast cancer. Yet there are real concerns about the Gail Model's ability to predict risk in populations other than white US women (and even among these women it has accuracy problems).
Learn more about risk reduction options for women with a Gail risk score of 1.66 or higher.
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Inherited Mutations and Breast Cancer Risk
Women who have inherited a breast cancer mutation are at higher than average risk for developing breast cancer. Between 5 and 10 percent of all breast cancer cases occur in women with a genetic mutation.
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Family History and Breast Cancer Risk
Approximately 25 percent of women with breast cancer have a family member with the disease. Some of these women carry a genetic mutation, but most do not. Why these other families are at higher risk is not yet fully understood.
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