All breast cancer results from changes in genes, but not all changes in the genes
are inherited. In fact, only about 5 to 10 percent of breast cancers are thought to
be caused by inheritance. Scientists have identified some of the genetic
alterations, or mutations, that are responsible. In particular, women with
mutations in genes called BRCA 1 or BRCA 2 (for breast cancer 1 or 2) are in
greater danger of breast cancer. Statistics indicate that about 50 to 60 percent of
women with a mutation in either gene will develop breast cancer by the age of 70.
These mutations also increase a womans risk of ovarian cancer, and possibly of
colon cancer. And they tend to promote development of breast cancer at a
younger than average age.
Women with an abnormal AT (ataxia telangiectasia) gene are also thought to be
at increased risk of breast cancer. Likewise, abnormalities in the p53 tumor
suppressor gene can increase a womans risk. Theres also some evidence that
women of Ashkenazi Jewish descent may be at higher risk of carrying a genetic
mutation associated with breast cancer.
Its important to remember that a case of breast cancer in your family does not
automatically mean that you carry a gene associated with the disease. After all,
breast cancer is relatively common in women without a genetic mutation. A family
history of both breast and ovarian cancer increases the likelihood that you carry
such a mutation, but does not guarantee it.
You can find out whether you have the BRCA 1 or BRCA 2 mutation by getting
a blood test. If you have a family history of breast cancer, theres good reason to
be tested, but there are pluses and minuses to knowing for sure. Confirmation of
the abnormality can alert you to the need for lifestyle changes you might otherwise
have dismissed. It can also weigh heavily in the decision to undergo drug therapy
or a mastectomy to reduce the risk of breast cancer (see chapter 37 for more
details). On the other hand, a positive reading could result in loss of health
insurance, inability to obtain insurance, or an increase in premiums to an