Breast cancer: Your genes

Women with a family history of breast cancer account for five per cent to ten per cent of all women with the disease. Having a first-degree relative (mother, sister or daughter) with breast cancer poses the greatest risk to other female members of the family -- doubling the risk compared to that of the general population.

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

• Diagnosis of breast cancer before the age of 50.
• Several family members diagnosed with breast and/or ovarian cancer.
• Diagnosis of bilateral breast cancer (cancer in both breasts).
• If there are men in the family who have had breast cancer.

What are the "breast cancer genes?"

Each of us is born with two copies of about 100,000 different genes contained in each cell. Genes are tiny segments of DNA that control how cells function, such as telling them when to divide and grow. One copy of each gene comes from your mother; the other is from your father.

A gene can develop an abnormality that changes the way the cell works. Abnormalities in two genes - BRCA1 and BRCA2 - have been found in some women with breast cancer. Over 200 mutations of these genes exist. Specific mutations in these genes are associated with an increased breast cancer risk.

An estimated 1 in 800 women carries the BRCA1 gene abnormality (the number of carriers of BRCA2 abnormality remains unknown). Women with inherited changes in either of these genes have 50 to 80% chance of developing breast cancer in their lifetime.

The risk of developing a second breast cancer among individuals carrying the BRCA1 gene abnormality is 65%. Bilateral breast cancer (cancer in both breasts) is also common in women who carry the mutated form of this gene.

Although less is known about the BRCA2 gene, scientists do know that mutations in the gene are associated with a similar risk of developing breast cancer among carriers. Alterations in the BRCA2 gene may also account for a small percentage of male breast cancer.

Mutations in 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 a changed or mutated 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.