HER2-positive breast cancer is not inherited. HER2 is a genetic mutation that occurs after conception. Doctors test for HER2 because they may treat your breast cancer differently if it’s positive.

Although inherited genes can cause breast cancer, they aren’t always the cause. Only 5–10% of breast cancers are related to inherited genes. Breast cancer can also be caused by gene mutations that are not inherited.

Human epidermal growth factor receptor 2 (HER2) is a gene that creates HER2 proteins. HER2 proteins are found on the surface of breast cells and promote breast cell growth.

In a healthy breast cell, HER2 is responsible for repairing the cell and growing more cells. If the HER2 gene is mutated, it causes an abnormal increase in the amount of HER2 proteins on the surface of the cells.

This causes cells to grow and divide out of control, which may lead to cancer. About 20–30% of breast cancers are HER2-positive, meaning the HER2 gene doesn’t function correctly.

HER2-positive breast cancer is not inherited. Instead, it’s considered a somatic genetic mutation. This type of mutation occurs after conception. Having a close relative with HER2-positive breast cancer does not increase your risk for breast cancer or HER2-positive breast cancer.

HER2-positive breast cancers are sometimes more aggressive than other types of breast cancer. If you’ve been diagnosed with breast cancer, your doctor may conduct a test to determine if your breast cancer is HER2-positive. If so, this will affect your treatment course.

Two types of tests can determine your HER2 status: the immunohistochemistry assay (IHC) and the in situ hybridization test (ISH). These tests are performed on a sample of the tumor.

HER2 tests are sometimes inaccurate, especially if they are not strongly HER2 positive or negative.

Inaccuracies may also happen because the sample tested was negative for HER2, but another area of the tumor may be HER2 positive.

Talk with your doctor about their confidence in your test results. If you’re concerned, or if your results are inconclusive, you can ask for a second HER2 test.

If your cancer is HER2-positive, a doctor typically recommends specific and targeted therapies to treat it.

Some inherited breast cancer cases can be traced to what is called breast cancer gene one (BRCA1) or breast cancer gene two (BRCA2).

Everyone has both BRCA1 and BRCA2 genes. Like the HER2 gene, they’re designed to repair cell damage and help restore normal, healthy breast cells. But in some people, these genes stop working properly. This increases the risk of breast cancer.

These abnormal gene mutations can be passed from generation to generation. If you’ve had a mother, grandmother, sister, or aunt with breast cancer or ovarian cancer before age 50, you may be more likely to have the mutated gene.

During their lifetime, women with a mutation in the BRCA1 or BRCA2 gene can have up to a 72% risk of being diagnosed with breast cancer. However, having the mutated gene doesn’t guarantee you’ll develop breast cancer.

Many other genes have been found to be related to an increased risk of breast cancer, including:

  • TP53
  • ATM
  • PALB2
  • PTEN
  • CHEK2

A genetic test can tell you if you have any mutations in genes that are related to an increased risk of breast cancer. A doctor may recommend genetic testing if you have:

  • a strong family history of breast cancer
  • a strong family history of ovarian cancer
  • a prior breast cancer diagnosis
  • another prior cancer diagnosis

If you’d like to be tested, you can contact a doctor or hospital education office. You can ask for a recommendation for a genetic counselor to make an appointment. They can discuss the risks of undergoing genetic testing and find out if your insurance covers the test.

Your genes may affect your risk for breast cancer, but your lifestyle can have an impact as well. Whether or not you have a genetic mutation, some preventive measures can help lower your risk. These include:

Maintain a moderate weight

People with overweight or obesity may have a higher risk of developing breast cancer and other cancers. Many factors can affect your ability to maintain a moderate weight. A doctor can help determine what a moderate weight for you is and how to maintain it.

Eat well

A nutritious and varied diet can help you maintain a moderate weight, and it also provides your body with plenty of vitamins, minerals, and nutrients it needs to stay well. To get the most benefit from your diet, focus on whole foods and avoid too many ultra-processed foods.

Exercise regularly

Being physically active can help you achieve and maintain a healthy weight. Exercise also reduces your risk for certain diseases, including:

  • cancer
  • heart disease
  • depression

Try to quit smoking, if you smoke

People who smoke are more likely to develop breast cancer.

Reduce your alcohol consumption

Drinking alcohol, including wine, beer, and spirits, may increase your risk for breast cancer and other types of cancer.

Is HER2-negative breast cancer genetic?

About 5–10% of breast cancers may be due to inherited genetic mutations. HER2-positive breast cancer is not inherited but forms due to genetic mutations that may occur after conception.

Who is more likely to have HER2-positive breast cancer?

HER2-positive breast cancer is due to a mutation that forms after conception. Inherited genetic factors do not increase your risk of having HER2-positive breast cancer.

What causes breast cancer to be HER2-positive?

HER2-positive breast cancer occurs due to a mutation in the human epidermal growth factor receptor 2 gene. This mutation is not genetically inherited.

Is HER2 a gene or receptor?

HER2 is the human epidermal growth factor receptor 2 gene. A mutation in this gene can cause an increase in the number of HER2 proteins on the surface of the cells.

HER2-positive breast cancer is not hereditary, but some other types of gene mutations related to breast cancer are inherited. Genetic testing can tell you if you have any of the mutations currently known to increase the risk of breast cancer or other cancers.