BRCA Genes and Breast Cancer

You may have heard about the genes BRCA1 (BReast CAncer gene 1) and BRCA2 (BReast CAncer gene 2). Despite their names, these genes actually help stop cells from growing and dividing too fast or in an uncontrolled way.

Everyone has two copies of these genes — one copy inherited from each parent. If one of your parents has a BRCA gene mutation, you have a 50% chance of inheriting a copy of the mutated gene.

If BRCA1, BRCA2, or both genes are damaged (or mutated), the genes have a harder time stopping out of control cell growth. This can lead to cancer.

People who inherit a BRCA1 or BRCA2 mutation have a higher risk of several types of cancer, especially breast and ovarian cancer. They also tend to develop cancer at a younger age than people without a mutation.

Some doctors use the term “hereditary breast and ovarian cancer syndrome,” or HBOC, when people inherit a BRCA mutation.

Still, not everyone who inherits a BRCA mutation develops cancer.

For breast and ovarian cancer, a BRCA1 mutation tends to increase risk more than a BRCA2 mutation. For prostate cancer, a BRCA2 mutation increases risk more than a BRCA1 mutation. This risk differs from person to person  depending on where in the gene the mutation is, as well as any other risk factors you might have.

According to the U.S. National Cancer Institute and the National Comprehensive Cancer Network, 60%-72% of women with a BRCA1 mutation and 55%-69% with a BRCA2 mutation will develop breast cancer during their lifetimes. In comparison, about 13% of women in the general population will develop breast cancer during their lifetimes.

If a woman with a BRCA mutation is diagnosed with breast cancer, she has a higher risk of developing breast cancer in the opposite breast, called contralateral breast cancer by doctors. In the 20 years after their first diagnosis, about 30%-40% of women with a BRCA1 mutation and about 25% of women with a BRCA2 mutation will develop cancer in the opposite breast. About 8% of women without a BRCA mutation will develop contralateral breast cancer.

Up to 1.2% of men with a BRCA1 mutation and between 1.8% and 7.1% with a BRCA2 mutation will develop breast cancer by age 70. Only about 0.1% of men in the general population develop breast cancer by age 70.

Research also shows that people with a BRCA1 or BRCA2 mutation with a history of breast cancer have a higher risk of developing a second primary cancer than people without the mutation

Between 39% and 58% of women with a BRCA1 mutation and 13% to 29% of women with a BRCA2 mutation will develop ovarian cancer during their lifetimes. This includes fallopian tube cancer and primary peritoneal cancer (abdominal lining) cancer. About 1.1% of women in the general population will develop ovarian cancer during their lifetimes.

Up to 5% of people with a BRCA1 mutation and between 5% and 10% of people with a BRCA2 mutation will develop pancreatic cancer during their lifetimes, compared to about 1.7% of people in the general population.

Between 7% and 26% of men with a BRCA1 mutation and 19%-61% with a BRCA2 mutation will develop prostate cancer by age 80, compared to about 10.6% of men in the general population.

People who inherit mutations in both copies of their BRCA1 or BRCA2 genes may develop types of Franconi anemia, a rare syndrome linked to developing solid tumors and acute myeloid leukemia, a type of blood cancer, often in childhood.

Studies have found more than 3,700 mutations linked to disease in the BRCA genes, some of which are more common in people of certain racial or ethnic backgrounds. For example, about 2% of people of Ashkenazi Jewish descent inherit specific types of BRCA mutations, according to the National Cancer Institute. Black people in the United States tend to have BRCA mutations that aren’t common in other racial or ethnic groups.

Inherited mutations in other genes are also linked to breast cancer, ovarian, and other cancers. Although these mutations aren’t as common as BRCA mutations, several of them are linked to a greater than 50% lifetime risk of breast cancer.

If you have a family history of breast or ovarian cancer, or have been diagnosed with breast cancer, you may be considering genetic testing. A good place to start is by asking your doctor for a breast cancer risk assessment. The results can help you decide if you’d like to meet with a genetic counselor to discuss testing.