Breast Cancer Genes Explained: How & When To Get Tested

Breast cancer is the most common cancer in women after skin cancer — and up to 15% of people with breast cancer have a genetic or inherited cause for the disease.

Researcher Charis Eng, MD, PhD, explains what you need to know about breast cancer genes and genetic testing.

What genes are linked to breast cancer?

The term “breast cancer genes” means genes that, when altered (mutated), increase your risk of getting breast cancer. These gene mutations shut down some of your natural cancer-fighting genes. When you don’t have your full army of genes fending off cancer, your risk of certain cancers goes up.

“BRCA1 and BRCA2 are the most common breast cancer genes when mutated, followed closely by PTEN mutations,” says Dr. Eng. “But several other breast cancer gene mutations exist. We know of at least 14 different genes right now, and we are currently exploring several others, too.”

These gene mutations aren’t limited to breast cancer risk. Some of these gene mutations may also increase the risk of:

• Colorectal cancer
• Endometrial/uterine cancer
• Melanoma
• Metastatic prostate cancer
• Ovarian cancer
• Pancreatic cancer
• Thyroid cancer

How common are breast cancer gene mutations?

“Breast cancer gene mutations aren’t common in the general population,” Dr. Eng says, “but they are common in people who have breast cancer. About 10% to 15% of people with breast cancer have one of the breast cancer gene mutations.”

You can inherit these gene mutations from either of your biological parents, and the cancers they’re linked to can affect both men and women — so consider all your relatives when thinking about your family history.

Who should get breast cancer genetic testing?

Genetic testing is the only way to know whether you have a breast cancer gene. These blood tests check for BRCA1 and BRCA2, as well as other known breast cancer genes.

If you have already been diagnosed with breast cancer, you may need genetic testing if you:

• Are of Ashkenazi Jewish descent
• Your sex recorded at birth was male
• Have a family history of breast cancer, especially if the relatives were male or under age 45 when they were diagnosed
• Have a family history of ovarian, pancreatic or prostate or other (e.g. thyroid) cancer
• Have a second breast cancer (not a recurrence of the first cancer)
• Have triple-negative breast cancer that was diagnosed before you were 60
• Were diagnosed with breast cancer at age 45 or younger

If you haven’t been diagnosed with breast cancer, consider genetic testing if:

• Your sex recorded at birth was male and you have been diagnosed with pancreatic cancer or high-grade metastatic prostate cancer
• You have a close family member with cancers, including ovarian cancer, pancreatic cancer or metastatic prostate cancer
• You have a known family history of the BRCA (or other) gene mutations
• You have a male relative with breast cancer or a female relative with cancer in both breasts
• You have been diagnosed with ovarian or pancreatic cancer
• You have family members who were diagnosed with breast cancer before age 45
• You have more than one family member with breast cancer

Genetic tests are helpful for people with risk factors, but not everyone needs them.

“Testing everyone in the general population would be like trying to find a needle in a haystack,” Dr. Eng says. “Most people would get negative results. And right now, the world doesn’t have enough geneticists to see all those patients and do a follow-up. Knowing your family history is important because it tells us who needs to be tested or if you need to be tested.”

How do I get tested for BRCA and other genes?

If your doctor finds that you’re at risk for hereditary breast cancer, they will refer you to a genetics professional, such as a genetic counselor, for genetic evaluation and pre- and post-test genetic counseling. Then, your blood is drawn and sent to a clinical lab for genetic analysis.

A geneticist (genetics expert) reads your blood test results and follows up with your provider. If you have a positive result, you’ll meet with your genetic counselor to discuss next steps for your care.

What your breast cancer genetic tests results mean

Having a positive genetic test result doesn’t mean you’ll get cancer. It means you have a higher risk of getting breast cancer than people without the mutation.

Consider these statistics:

• Women without breast cancer gene mutations have a 12% lifetime risk of breast cancer.
• Women with a BRCA mutation have up to an 80% lifetime risk of breast cancer.
• Women with the PTEN mutation have an 85% lifetime risk.
• Men with the BRCA2 mutation have about an 8% lifetime risk, 80 times greater than males without the mutation.

Even if you get tested and get a negative result, don’t skip mammograms or other health screenings, and continue to follow the American Cancer Society’s guidelines.

“Most cases of breast cancer aren’t hereditary,” says Dr. Eng. “A negative result means you don’t have the known gene mutations for breast cancer. But you can still get breast cancer.”

How your test results can help you

A positive result for breast cancer genes can be difficult to deal with. But you can use this information to your advantage.

“If we know you have a breast cancer gene alteration, we can take extra steps to catch cancer early, when it’s most treatable,” Dr. Eng says. “Your providers can perform enhanced screenings starting at an early age, usually 25 or 30, depending on the gene. Knowledge is power.”