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What to Know if You're Considering Genetic Testing

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by Jamie DePolo

If you and/or some members of your family have been diagnosed with breast cancer, you may be considering genetic testing. Genetic testing is available to identify changes, called mutations, in genes that have been linked to an increased risk of breast and other cancers.

Three of the most well-known genes that can mutate and raise the risk of breast and/or ovarian cancer are BRCA1, BRCA2, and PALB2. Mutations in other genes are also associated with breast cancer. These genetic mutations are much less common and don’t seem to increase risk as much as BRCA1, BRCA2, and PALB2 mutations.

Women who inherit a mutation in the BRCA1, BRCA2, or PALB2 genes -- from their mothers OR their fathers -- have a much higher-than-average risk of developing breast cancer and/or ovarian cancer. (Abnormal PALB2 genes are suspected to raise the risk of ovarian cancer, but larger studies need to be done to confirm that risk.) Men with these mutations have an increased risk of breast cancer, especially if the BRCA2 gene is affected, and possibly of prostate cancer. Many inherited cases of breast cancer have been associated with mutations in these three genes.

Still, it’s important to know that only about 5% to 10% of breast cancers are thought to be hereditary, meaning they’re caused by one of these genetic mutations passed from parent to child.

“In the general population, there is a pretty low risk of having an inherited gene mutation linked to breast cancer,” said Cristina Nixon, M.S., a licensed certified genetic counselor with the Cancer Risk Assessment and Genetic Program at Main Line Health in Pennsylvania. “BRCA1 and BRCA2 are the most common genes associated with hereditary breast cancer, and in the general population, the chances of carrying a mutation in either of those genes is anywhere between 1 in 500 to 1 in 800. So, it’s pretty low. There are certain ethnicities where that rate is higher, specifically in individuals who are of Eastern European Jewish decent, also known as Ashkenazi Jewish individuals. They have a carrier rate of 1 in 40. So, 1 in 40 individuals will carry a mutation in BRCA1 or BRCA2.”

Finding out if you carry a genetic mutation linked to a higher risk of breast cancer can help you make lifestyle choices to keep your risk as low as it can be, including:

  • maintaining a healthy weight
  • exercising regularly
  • limiting alcohol
  • not smoking

Along with lifestyle choices, there are other risk-reducing options for women at high risk because of a genetic mutation, including:

  • more frequent screening
  • taking hormonal therapy medicines preventively
  • protective surgery

Getting started

The best way to start the genetic testing process is to learn more about your family history on both your mother’s AND your father’s side. A genetic mutation is more likely to run in your family if:

  • Three or more women in your family have had breast and/or ovarian cancer, particularly if breast cancer is diagnosed at a younger age than this cancer typically develops (before age 50).
  • A close relative has had cancer involving both breasts.
  • There is both breast and ovarian cancer in your family.
  • Men in your family have had breast cancer.
  • There is breast cancer in your family and either male relatives on the same side of the family have had prostate cancer at a young age, or male or female relatives on the same side of the family have had other types of cancer, including but not limited to melanoma, pancreatic, stomach, uterine, thyroid, colon, and/or sarcoma.
  • Your family is of Ashkenazi (Eastern European) Jewish descent.

You may want to meet with a genetic counselor, a medical professional specially trained to understand and provide information about genetics and disease. A genetic counselor can help you build a family tree that shows all of the cases of breast, ovarian, and other types of cancer in your family, along with the ages at which they occurred.

“When we take a family history as a genetic counselor, or even with your physicians or nurses, whoever is asking about cancer family history, it’s important to tell them about all of the cancer in the family, not just breast cancer,” Nixon explained. “Even if breast cancer is your main concern, we still want to know about all of the cancer in the family because it really helps to guide what genes we focus on when we’re talking with you about genetic testing. Genetic testing for hereditary breast cancer has expanded so much beyond just BRCA1 and BRCA2.”

How does genetic testing work?

Genetic testing is usually done on a blood or saliva sample taken in your doctor’s office and sent to a commercial lab or a research testing facility. During testing, the genes are separated from the rest of the DNA and scanned for mutations.

People who opt for genetic testing may choose to be tested for only BRCA1 and BRCA2 mutations or to be tested for multiple breast cancer-related genes through what’s called a panel test.

Testing positive when you don’t have cancer

Testing positive for a genetic mutation linked to breast cancer doesn’t mean that you’ll be diagnosed with cancer. It means that you have a much higher-than-average risk of developing it over the course of your lifetime.

The average lifetime risk of breast cancer for women is about 12%. If you have a BRCA1 or BRCA2 mutation, the risk of developing breast cancer in your lifetime is about 69-72% -- about 6 times greater than that of a woman who doesn’t have the mutation. Your lifetime risk of ovarian cancer is significantly elevated as well: 17% to 44%, versus just under 2% for the general population.

Men with BRCA mutations are considered to have a higher lifetime risk of male breast cancer, especially if the BRCA2 gene is affected. One study found that men with a BRCA2 mutation have a 7% lifetime risk of developing breast cancer. They are also at increased risk of developing prostate cancer.

Women with a PALB2 mutation have a 33% to 58% lifetime risk of developing breast cancer. Research on the PALB2 gene is ongoing: While the risk for male breast, pancreatic, and ovarian cancers is thought to be increased, the exact amount of increase is still being studied.

Whether you are a man or a woman, a BRCA1, BRCA2, or PALB2 mutation means there is a 50% chance you could have passed that specific mutation on to your children.

Testing positive when you’ve been diagnosed with breast cancer

If you’ve been diagnosed with breast cancer and your genetic test results come back positive for a mutation linked to breast cancer, your doctor will work with you to figure out how your genetic status might affect your treatment decisions.

If you’ve been diagnosed with early-stage disease, you’ll also want to talk to your doctor about reducing the risk of a new, second breast cancer or ovarian cancer. Women who’ve been diagnosed with breast cancer and have a BRCA1, BRCA2, or PALB2 mutation have a much higher risk of developing a new, second breast cancer, as well as ovarian cancer. Some women choose to have risk-reducing surgery, such as removing the other healthy breast and/or the ovaries.

If you’ve been diagnosed with metastatic breast cancer and learn you have a BRCA mutation, you may benefit from treatment with a new type of targeted therapy called a PARP inhibitor.

DNA carries genetic information in both healthy cells and cancer cells. Cells can develop DNA damage spontaneously or from exposure to specific things in the environment (too much sun, for example) that make DNA damage more likely to happen. But cells can detect and repair damage to DNA. When DNA is damaged in a healthy cell and the damage isn't fixed, that cell can become cancerous. Mutated BRCA1 and BRCA2 genes are thought to increase the risk of breast and other cancers because these abnormal genes interfere with cells' ability to repair damaged DNA.

The poly ADP-ribose polymerase (PARP) enzyme fixes DNA damage in both healthy and cancer cells. Research has shown that Lynparza (chemical name: olaparib), which interferes with (inhibits) the PARP enzyme, makes it even harder for cancer cells with an abnormal BRCA1 or BRCA2 gene to fix DNA damage. So, a PARP inhibitor like Lynparza makes certain cancer cells less likely to survive their DNA damage. Lynparza is specifically approved to treat metastatic, HER2-negative breast cancer in women with a BRCA mutation.

Variants of uncertain significance

In a small number of cases, genetic testing finds a “variant of uncertain/unknown significance,” or VUS. This means there is a portion of the gene that looks different from the way it’s normally expected to look. However, researchers haven’t yet confirmed whether this variant is a harmless change or a risk factor for cancer. The variant remains on a “watch list” as researchers collect information to determine whether or not people who have it are at higher risk for cancer.

“That’s also part of the counseling up front before you have testing,” Nixon explained, “is to also be aware that an inconclusive result is a possibility.”

The takeaway

While only about 5% to 10% of breast cancers are related to a genetic mutation, knowing if you carry a genetic mutation linked to a higher risk of breast cancer can help you make lifestyle choices to keep your risk as low as it can be. These include maintaining a healthy weight, exercising regularly, and limiting alcohol.

In addition to lifestyle choices, women at high risk of breast cancer because of a genetic mutation can take other steps, including more frequent screening and taking hormonal therapy medicines preventively, as well as more aggressive steps, such as protective surgery.

If you’ve been diagnosed with breast cancer, testing positive for a genetic mutation may influence your treatment choices.

Learn more about genetic testing in's podcast series with Cristina Nixon: Genetics, Genetic Testing, and Breast Cancer.

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