Genetics of Breast Cancer

Women with a genetic risk for breast cancer account for five to ten percent of all women with the disease. Having a first-degree relative (mother, sister, daughter) with breast cancer poses the greatest risk to other female members of the family – three to five times that of the general population.

Several characteristics may suggest that a woman has a breast cancer gene:

• Diagnosis of breast cancer before age 40
• Several family members diagnosed with breast and/or ovarian cancer
• Diagnosis of bilateral breast cancer (cancer in both breasts)

What are the "Breast Cancer Genes?"

Sometimes a gene can develop an abnormality that will change how the cell works. More than one faulty gene has been found in women with breast cancer.

BRCA1 was the first gene detected that increased a woman's risk for breast and ovarian cancer. The presence of this gene produces a greater than 80 percent risk of developing breast or ovarian cancer by age 85. An estimated one in 600 women carry this gene. The risk of developing a second breast cancer among individuals carrying the BRCA1 gene is 65 percent. Bilateral breast cancer (cancer in both breasts) is also common in women who carry this gene.

A second gene, BRCA2, also plays a major part in breast cancer. Less information is available on the function of this gene; however, scientists do know that it is associated with a similar risk of developing breast cancer among carriers. BRCA2 may also account for some small percentage of male breast cancer.

BRCA1 and BRCA2

Both the BRCA1 and BRCA2 genes can be inherited from either parent. Therefore, the father's family history of breast cancer is also important. Men or women who carry one of these gene mutations have a 50/50 chance of passing it on to each of their children.

Usually, these BRCA genes help to prevent cancer by creating proteins that keep cells from growing abnormally. But, if an abnormal BRCA1 or BRCA2 is inherited, you may be more susceptible to developing cancer during your lifetime. In addition, women with an altered BRCA gene usually have an increased risk of developing breast cancer at a younger age (before menopause). However, it's important to note that not all women who carry these genes will develop cancer.

At-risk families can take blood tests to screen for mutations in these genes. However, genetic testing is done only when definitely indicated by a strong personal or family history. Genetic testing may also be used to determine if a woman who has already been diagnosed with breast cancer is at an increased risk for a second breast cancer or ovarian cancer.

For more information on breast cancer, download the Free Breast Cancer Treatment Guide.