Breast Cancer: The Genetic Connection

By: Linda T. Vahdat, MD
By: Gladys Rosenthal MS, CGC
Genetic sources of disease are being explored like never before. The search for genetic explanations of breast cancer is no exception, and the "breast cancer genes." BRCA-1 and BRCA-2 have received a great deal of attention in the media. But did you know that only about ten percent of breast cancers are linked to mutations in these genes.
Below, two experts in breast cancer genetics offer basic information about the role heredity plays in cancer risk.

First, what is a gene?
GLADYS ROSENTHAL, MS: A gene is the basic unit of heredity. Our genes are the blueprints for our appearances, and are also our blueprints for housekeeping functions, or all the processes that our body has to go through in order to keep going. We each have two genes for each trait. Our genes come in pairs: one from our mother, one from our father. So that half of our hereditary material comes from the maternal side and half from the paternal side.

What are the "breast cancer genes"?
GLADYS ROSENTHAL, MS: There are two genes that are associated with breast cancer and ovarian cancer: breast cancer gene #1, or BRCA-1, and breast cancer gene #2, or BRCA-2.


Each of us has two BRCA-1 genes and two BRCA-2 genes. These genes are tumor suppressor genes, or blueprints for specific proteins that are involved in tumor suppression. If there is a change, or mutation, in one of these genes, the protein that the gene makes will be damaged. That damage to the gene compromises its ability to perform the function of tumor suppression.

If a woman has a mutation in one of the breast cancer genes, what is her risk of developing cancer?
LINDA VAHDAT, MD: She?s absolutely not destined to develop cancer. One of the things that we?ve learned about breast cancer is that there are many risk factors. Having a mutation in either the BRCA-1 or BRCA-2 gene can certainly increase the susceptibility. But there have been many studies done, and I believe that it is still accepted that, for women with a mutated gene, the range on the lifetime risk of breast cancer development is between 50 to 87 percent. It is not 100 percent.

What are some other risk factors for breast cancer?
LINDA VAHDAT, MD: There are a number of risk factors for breast cancer. Certainly the biggest risk factor is increasing age and that?s why we see statistics such as one in eight lifetime risk for development of breast cancer. But a woman of 25 doesn?t have a one in eight risk of developing breast cancer. It?s probably one in several thousand. So the biggest risk factor is increasing age.

Family histories play a role as well. If you have a first-degree relative -- a mother or a sister -- who has breast cancer, this can increase your risk of developing breast cancer. There are certain reproductive risk factors, early onset of menstruation, late menopause, and late age at first full-term birth...these things all factor into the risk equation.

So what should women who are an increased risk of hereditary breast cancer do?
LINDA VAHDAT, MD: I think that women who are at risk for hereditary breast cancer clearly have an increased risk over women in the general population. They should consider entering clinical trials not only for surveillance, but for chemoprevention with medications like tamoxifen, if it?s appropriate.

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