What is the BRCA1 gene? Why Angelina Jolie got a double mastectomy

Angelina Jolie announced Tuesday that she underwent a double mastectomy to reduce her risk of contracting breast cancer.

Penning an op-ed in The New York Times titled "My Medical Choice," Jolie said she made the decision to undergo the preventative surgery, which removes healthy breast tissue before it becomes cancerous, after finding out she was a carrier for a gene that makes her far more prone to cancer.

Jolie carries what she called a "faulty" gene, known as BRCA1, and her doctors estimated she had an 87 percent risk of breast cancer and 50 percent risk of ovarian cancer.

More from GlobalPost: Angelina Jolie: I had a double mastectomy

What is BRCA1 and how many women are carriers?

The official name of this gene is "breast cancer 1, early onset." BRCA1 and BRCA2 are human genes that are known as tumor suppressors. Mutation of these genes has been linked to higher rates of breast and ovarian cancer.

Often, close family members who share the gene will be diagnosed with higher rates of these cancers. Jolie's mother died of cancer at age 56.

The genes can be found in both men and women.

According to the National Cancer Institute, about 12 percent of women in the general population will develop breast cancer sometime in their lives.

About 60 percent of women who inherited a harmful mutation in BRCA1 or BRCA2 will develop the disease, making them about five times more likely to develop breast cancer than a woman who does not have a mutation.

The number of women who are carriers of the gene mutation is still small. Only 3 to 5 percent of women who develop breast cancer have a BRCA mutation.

How do you test for it?

A blood test can tell you if you're a carrier for the BRCA1 gene.

The cost for the test usually ranges from several hundred to several thousand dollars and isn't commonly covered by insurance.

Jolie said the cost of getting tested for BRCA1 and BRCA2, which can be more than $3,000 in the United States, "remains an obstacle for many women."

Who should get tested?

Genetic testing can be expensive and isn't recommended for all women. Since the gene is relatively rare, only those with several risk factors should consider genetic testing.

The Susan G. Komen foundation recommends that anyone with a personal history of breast cancer at age 50 or younger, a family history of male breast cancer, or cancer in both breasts consider testing.

History of breast or ovarian cancers on both sides of the family, and a personal history of triple negative breast cancer (breast cancer that is estrogen receptor-negative, progesterone receptor-negative and HER2/neu receptor-negative) are also indicators of risk.

The Office of the Surgeon General and the National Human Genome Research Institute have an online tool called "My Family Health Portrait" that can help you track your family's history.

What are the options after finding out you're a carrier?

Early cancer screening can help find cancer early, when it may be most treatable. Regular mammograms and clinical breast exams may catch the cancer early enough to be successfully treated.

A mastectomy, like the one Jolie decided to undergo, can remove at-risk breast tissue and reduce the risk of contracting cancer.

But because not all of the tissue can be removed, some women might still develop breast cancer, ovarian cancer, or primary peritoneal carcinomatosis (a type of cancer similar to ovarian cancer) even after this type of surgery.

The National Cancer Institute also says there are several drugs, both natural and synthetic, that can reduce the risk of developing cancer or reduce the chance that cancer will come back.

Tamoxifen was approved by the FDA as a breast cancer treatment after it was found to reduce the risk of developing breast cancer by about 50 percent in women who are at increased risk.