Women with a genetic risk for breast cancer account for five to
10 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"?
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 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.
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.