Breast Cancer Screening
How important is a family history of breast cancer?
Many women believe that their own risk of developing breast cancer is higher than it actually is. Those with a family history of breast cancer frequently guess that their risk is much, much higher than it really is. Most women who have relatives with a history of breast cancer (even several relatives) have no personal excess risk of cancer. The group of women who have a mother and/or sister who has had breast cancer includes subcategories with different risk profiles.
Hereditary/Genetic Breast Cancer Risk
An extremely small fraction of women—less than 1/2 of 1%—have a specific mutation on one of the two identified genes that affect breast cancer risk—BRCA1 and BRCA2. There is a likelihood that other genes will be identified that, when carrying specific mutations, increase a woman's chance of getting breast cancer. These are yet to be discovered. None of the so called "breast cancer genes" are really breast cancer genes—in the sense that the function of the gene is to cause breast cancer. All women have BRCA genes. Some women have mutations in their BRCA genes that cause the gene to malfunction. These specific mutations increase a woman's risk of developing breast cancer. Why? When the gene is functioning, as it does in most women, it acts as a tumor suppressor to stop damaged cells from growing out of control. When the gene is malfunctioning it doesn't provide this protection. Certain family lines have been identified in which the BRCA genes have become mutated. Those mutations are carried in the germ line cells—the egg and sperm—and, hence, are passed down from parent to offspring. Again, these hereditary mutations are extremely rare.
Elevated Familial Breast Cancer Risk
A larger group of women may be at moderately higher risk for familial breast cancer, meaning that breast cancer affects one's relatives across several generations at an above-average rate, but no specific cancer-related genes are involved. The somewhat-higher risk could be related to things that are partially inherited such as body size, a tendency to gain weight during the middle years, or naturally higher level of circulating (endogenous) estrogens. It could also be related to things that are socially inherited, rather than biologically inherited, such as preferences about family size, the proper age for marriage, and even food choices. A woman cannot change her genes, but she may be able to change other factors. For example, many women can control the amount of weight they gain between the ages of 30 and 60 by adopting specific diet and exercise plans. There are aspects of a familial tendency to breast cancer risk that can be changed by individual choices. Again, these choice will help reduce risk, but do not eliminate it.
History of Familial Breast Cancer with No Elevated Risk
The vast majority of women who have relatives with a history of breast cancer (even several relatives) have no personal excess risk of cancer. An adult woman can expect to live past the age of 80, on the average. By that age, 10% of all women with totally normal genes will have had breast cancer. Accordingly, their sisters, daughters, and granddaughters will have a "family history of breast cancer," even when nothing genetic is involved—just the ordinary average risk that goes along with having breasts in the first place. Our grandmothers' grandmothers did not have to deal with breast cancer nearly as frequently—because their life expectancies were much shorter. At the beginning of the century, on average, women only lived around 35 years after having a child, instead of another 60 years. As people live longer and mortality due to other causes decreases, more people will develop cancers. Hence, more of us will have relatives who have had cancer. A small percentage of these cancers will be due to a genetically inherited risk. The vast majority will not. Having a relative with breast cancer rarely means that you will have an increased risk of breast cancer.
