Who Gets Tested

If your family history of breast cancer suggests an inherited pattern, genetic testing may be considered. Genetic testing is most informative when it starts with a family member who has had an early-onset breast cancer or an ovarian cancer. This means that if you haven't had one of these cancers, and someone else in your family has, genetic testing will probably be more helpful if it starts with that person. Here's why:

• Not every person in the family will have the abnormal breast cancer gene. It's more likely that a family member with cancer will have the abnormality than one without cancer.
• Since not all genetic abnormalities can be identified, testing someone without cancer can be confusing. That person could have a normal gene because she or he did not inherit the abnormality. Or that person could have a normal gene test result because the family has an abnormality that cannot yet be identified.

Sometimes, there are no living relatives with cancer who can undergo genetic testing. A genetic counselor can help you decide who in the family is the best person to test and why.

If someone in your family has already undergone genetic testing and is found to have an abnormality in a breast cancer gene, any relative can be tested for that specific abnormality to learn whether or not she or he has also inherited it.

From a practical standpoint, it is best to test the relative who is most closely related to the person found to have the abnormal gene. If that person does not have it, she or he could not have passed it on to children. If the person in your family most closely related to the individual with the genetic mutation does not want to be tested or is deceased, you may want to proceed with your own testing anyway.

For example, if your mother's sister had a proven genetic abnormality, the next person to be tested would be your mother. If her test were negative (no gene abnormality present), then you would not need to be tested. If your mother's test were positive, you might then decide to be tested. If your mother is no longer living, then you might go ahead with testing on the basis of your aunt's test result.

Genetic testing typically is performed using a blood sample. If a woman with breast cancer has had a bone marrow transplant using bone marrow donated from another person, a sample of her blood won't necessarily represent her own genetic composition. In that situation, testing should be done on blood from a blood sample stored before the transplant, from a tissue scraping, or from a biopsy.

Testing children

Most experts advise against testing children under age 18 because no safe, effective therapies currently exist to help prevent breast cancer in girls so young. Furthermore, children should be old enough to decide for themselves whether or not they want information about their lifetime cancer risks.

It is also quite possible that by the time today's children reach adulthood, scientists will have discovered a new treatment to correct abnormal breast cancer genes before cancer has a chance to develop.