The Odds of Having Abnormal Breast Cancer Genes

Most women who get breast cancer do NOT have an inherited abnormal breast cancer gene. BRCA1 and BRCA2 abnormalities probably account for only about 10% of all breast cancers.

The abnormal breast cancer genes were first discovered in studies of families in which many young women were affected by breast cancer, ovarian cancer, or both.

You are substantially more likely to have an abnormal breast cancer gene if:

• You have blood relatives (grandmothers, mother, sisters, aunts) on either your mother's or father's side of the family who had breast cancer diagnosed before age 50.
• There is both breast and ovarian cancer in your family, particularly in a single individual.
• Women in your family have had cancer in both breasts.
• You are of Ashkenazi Jewish (family from Eastern Europe) heritage.
• You are of African American heritage and have been diagnosed with breast cancer at age 35 or younger.
• A man in your family has had breast cancer.

If one family member has an abnormal breast cancer gene, it does not mean that all family members will have it.

Suppose either your mother or father has a BRCA1 or BRCA2 abnormality. Your risk of inheriting the abnormal gene is 50%. Each of your children has a 25% chance of inheriting the abnormal gene — 50% of your 50% risk (as long as the children's father does not have an abnormal gene).

Abnormalities seen more in younger women

Breast cancer gene abnormalities are more commonly found in women diagnosed with breast cancer before age 40. As many as 25% of these women have an abnormal breast cancer gene — usually BRCA1 — regardless of their family history.

Gene abnormalities in Ashkenazi Jewish, Hispanic, and African American women

Specific abnormalities in the BRCA1 and BRCA2 genes are more commonly found in Ashkenazi Jewish women. Ashkenazi Jews have ancestors from Central or Eastern Europe.

About 1 in 40 Ashkenazi Jews — with or without breast cancer — has a genetic mutation in BRCA1 or BRCA2. In one study of more than 5,300 Ashkenazi Jewish men and women (New England Journal of Medicine, May 15, 1997), 120 people (2.3%) had one of the three specific abnormalities in BRCA1 and BRCA2 known to be associated with a higher risk of breast cancer.

A more recent study (Journal of the American Medical Association, December 26, 2007) of more than 3,000 women diagnosed with breast cancer looked at the risk of abnormal BRCA1 genes in different ethnicities. The results showed:

• 8.3% of Ashkenazi Jewish women had an abnormal BRCA1 gene.
• 3.5% of Hispanic women had an abnormal BRCA1 gene.
• 16.7% of African American women younger than age 35 who had been diagnosed with breast cancer had an abnormal BRCA1 gene.
• 2.2% of white women who were not Ashkenazi Jews had an abnormal BRCA1 gene.

This means that Hispanic women are more likely to have an abnormal BRCA1 gene than white women who are not Ashkenazi Jews and that younger African American women diagnosed with breast cancer are twice as likely to have an abnormal BRCA1 gene than Ashkenazi Jewish women.