Understanding Your Risk
Breast Cancer research can be difficult to understand. When trying to understand the outcomes of scientific studies that typically use statistical methods, there are many unfamiliar terms that can be overwhelming.
There are three kinds of risk commonly referred to when discussing breast cancer: absolute risk, relative risk, and attributable 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 one in eight for non-Hispanic white women.
Your absolute risk also depends to a great extent on your age.
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 a nation. 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 one in eight, or 12%, 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 one in 30, or 3.3%, which is significantly lower than the “average” risk of 12%.
If you call the risk of a 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 developed. 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%, which is the average 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% 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.