Breast Cancer Screening

What is a risk factor?

A risk factor for breast cancer is not the same thing as a cause of breast cancer. A risk factor is something that may increase your chance of getting breast cancer. It is very important to remember that having risk factors does not mean that you will get breast cancer. In fact, most women who develop breast cancer have none of the known risk factors, and most women who have several of the major risk factors never develop breast cancer.

To better understand what it means to be at a higher risk or a lower risk for breast cancer, let's consider an example. Divide a large population of 30-year-old women into a higher-risk group (those whose mother or sister has had breast cancer) and a lower-risk group (those with no family history). On the average, around 4 out of 1000 women in the lower-risk group would develop breast cancer during the 10 years before age 40, compared to around 7 out of 1000 women in the higher-risk group. Since 993 out of 1000 women with a family history will not develop breast cancer between the ages of 30 and 40, it would not be accurate to say that this group is at high risk for cancer -- merely somewhat higher than having no relatives at all with a history of breast cancer.

Researchers suspect risk factors whenever a study of large numbers of women shows a difference in the cancer rates between one group and another. Such a difference becomes a risk factor only after it is seen in most or all studies, and only if it is related directly to a cause of cancer. Women with graduate degrees have breast cancer more frequently than women with a high school education. This is a difference in risk levels that is consistent across many studies. However, higher education is not a risk factor for breast cancer because it has no direct impact on anything that can cause it. Women who only seek a high school education are more likely to marry earlier, begin their families earlier and have larger families. Women who choose to seek college and professional degrees frequently marry later and have smaller families. These decisions affect a woman's lifetime exposure to estrogen (which is a risk factor), while merely attending college does not. So education is connected to a difference in breast cancer risk, but it is not a direct connection. Therefore, it is not a risk factor for breast cancer.