Many factors can affect your risk of breast cancer—how much you exercise, your age, and more. But a key risk lies in your genetic code.

In most people, the genes known as BRCA 1 and BRCA 2 normally help protect against cancer. But in a small number of people—1 in 300 to 500 women—those genes can mutate and instead raise the risk of breast, ovarian, and other cancers.

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Women have a 12 percent chance of being diagnosed with breast cancer in their lifetime and a 1 or 2 percent chance of being diagnosed with ovarian cancer. A mutation on either BRCA 1 or 2 means the risk of both cancers is much higher: 45 to 65 percent by age 70 for breast cancer, and 10 to 39 percent by age 70 for ovarian cancer.

Since 1996, women have been able to take a simple blood or saliva test to see whether they have a BRCA mutation. Generally, a doctor will evaluate your family history and, if you meet certain criteria, refer you to a genetic counselor who will determine if you’re a candidate for a breast cancer genetic test.

Having the mutation can tell you a lot about your risk of developing cancer, and some women who test positive will opt for preventive measures such as “mastectomy, or oophorectomy [removal of the ovaries], or increased screening with MRI or mammogram,” says Fangjian Guo, M.D., Ph.D., assistant professor in the department of obstetrics and gynecology at University of Texas Medical Branch.

But the mutations are rare, and most inherited breast cancers aren’t caused by BRCA. (BRCA mutations account for a fifth to a quarter of inherited breast cancers, and only about 5 to 10 percent of all breast cancer diagnoses, according to the National Cancer Institute.)

Because these mutations are so uncommon, “the chance of a test result being a false-positive or false-negative is higher than desirable,” says David Flannery, M.D., medical director of the American College of Medical Genetics and Genomics. "Not everybody is a candidate for BRCA gene testing."

The test is much more likely to be accurate for women whose personal or family history already puts them at risk of having a BRCA gene mutation, he says. Also, without a family history that may indicate a BRCA mutation, it’s unlikely that your insurance will cover the test.

Here’s how to tell if you may benefit from a breast cancer genetic test.

Consider Your Personal and Family History

Not everyone who has had breast cancer or who has a relative with breast cancer needs to have a breast cancer genetic test.

You may be a candidate for genetic testing for BRCA mutations if any of your relatives know they carry a mutation. Or if you, or any of your first degree relatives—parents, siblings, and children—have any of the following:

  • A diagnosis of breast cancer at age 50 or earlier.

  • Triple negative breast cancer at age 60 or earlier.

  • More than one case of breast cancer or cancer in both breasts.

  • For those of Ashkenazi Jewish heritage, breast or ovarian cancer at any age. (BRCA mutations are more common in this group.)

  • A diagnosis of ovarian cancer.

If you have been diagnosed with breast, ovarian or pancreatic cancer, and two other relatives (including aunts, uncles, and cousins) on the same side of your family also have one of those cancers (or an aggressive prostate cancer), it may also be a sign that you’re a candidate for BRCA testing.

Finding out you have a genetic mutation can help your other family members decide if they should get tested, because they may be at higher risk. And even if you already have cancer, knowing your BRCA mutation status can inform the decisions you make about treatment. For instance, a woman with breast cancer and a BRCA mutation may consider removing her ovaries, to reduce the risk of ovarian cancer.

Seek Genetic Counseling

If you fit into one of the categories above, you still shouldn’t rush to get your blood or saliva tested. Instead, talk to your doctor, who can help you figure out if you’re a good candidate, and who can refer you to a genetic counselor—a healthcare professional trained to assess a family’s risk for inherited conditions.

The counselor will then perform a more involved cancer risk analysis for your family, to find out if testing is really necessary.

If your family is a candidate, the counselor can also help to determine the right family member to test, Flannery says. It may be beneficial to test a relative with a known cancer, because ruling out a mutation in that person can make it less important to test the rest of the family.

If it turns out you do carry a BRCA mutation, then the counselor can also help you figure out the next steps, including what, if any, action you want to take to reduce your risk, and whether your family members should also have a breast cancer genetic test.

Finally, remember that testing for BRCA mutations isn’t a perfect strategy, because even people with no family history of cancer can sometimes turn out to be carriers.