Cancer begins when the genes inside breast cells develop abnormal changes called mutations. In about 15 percent to 20 percent of breast cancer cases, tumor cells have a mutation that leads to HER2-positive breast cancer. HER2 status is a key piece of information that tells your cancer care team how your tumor may behave and grow.

HER2-positive breast cancer tends to grow faster than other types, but it also responds well to certain treatments. If your cancer is HER2-positive, your oncology team can better determine your prognosis (predicted outlook) and the most promising treatments for you.

In this article, we’ll cover the basics about HER2-positive breast cancer, including its genetic basis, tests that help detect HER2 status, and treatments for this type of breast cancer.

The HER2 Gene

The full name of the HER2 gene is human epidermal growth factor receptor 2, which has a few shortened forms:

• HER2 receptor
• HER2/neu
• HER2

The full name of the HER2 gene is human epidermal growth factor receptor 2.

The gene also goes by other names, such as ERBB2. “HER2-positive” is sometimes shortened to “HER2+” when describing breast cancer.

The HER2 gene makes a protein that’s also called HER2. When the HER2 gene is activated (turned on), it sends signals that tell the cell to grow. The cell then prepares to divide and produce new cells.

In HER2-positive breast cancer, the gene malfunctions and makes too many copies of the HER2 gene (called HER2 gene overexpression). Larger numbers of HER2 genes lead cancer cells to make higher-than-normal levels of the HER2 protein. As a result, the cancer cells grow too quickly, forming a tumor.

In 1987, researchers funded by the National Cancer Institute were among the first to recognize the significance of HER2 gene expression in breast cancer. They also discovered that HER2 status is linked to the risk of metastasis (cancer spreading to other areas) and recurrence (cancer coming back) and can affect survival rates. HER2 status has since become an essential piece of information in breast cancer diagnosis, prognosis, and treatment.

Finding out that your cancer is HER2-positive helps doctors understand why the cells are growing too fast and what treatments are most likely to work.

Is HER2 Genetic?

Cancer is a genetic disease. This simply means it’s a disease caused by mutations in genes. When you have cancer, there are changes in the genes that tell cells how to grow and multiply. These genetic mutations can be acquired over time or inherited from your parents. Most cancer is a result of acquired mutations that develop throughout life.

When a genetic mutation passes from parent to child and causes cancer, it’s called a hereditary disease. Changes in breast cancer gene 1 (BRCA1) and breast cancer gene 2 (BRCA2), for example, can be inherited from either parent. Inheriting this mutation doesn’t mean someone will develop breast cancer, but it increases their risk. Because a parent can pass the mutation to their child, breast cancers caused by BRCA1 or BRCA2 are both genetic and hereditary.

In the case of HER2, the gene mutation isn’t passed down from parent to child. Instead, the change happens over time and is called an acquired mutation. Researchers think this type of change may be linked to factors such as environment or lifestyle. That means HER2 is a genetic change, but not a hereditary one.

The HER2 gene mutation isn’t passed down from parent to child, so it’s not hereditary.

Testing for HER2

If you’ve been diagnosed with breast cancer, your care team will likely recommend testing your tumor for HER2 status. This testing can be performed on biopsy tissue or through a blood test. Other lab tests can also show whether your cells have proteins like hormone receptors that affect treatment.

The first step of breast cancer diagnosis and HER2 testing often involves a biopsy. During this procedure, a doctor removes a sample of breast tissue. A pathologist then examines the tissue using tests such as:

• Immunohistochemistry (IHC), which estimates the amount of HER2 protein on the outside of the cells
• Fluorescence in situ hybridization (FISH), which measures the number of HER2 genes inside the cells​

Together, these tests provide genetic details about breast cancer cells and, along with other lab tests, help build a complete picture of hormone receptor status. Read more about diagnostic tests for HER2-positive breast cancer.

If you are diagnosed with breast cancer, your care team will probably recommend you go through genetic testing to determine your HER2 status.

Treatments for HER2-Positive Breast Cancer

Regardless of your type of breast cancer, you may need treatments like:

• Surgery to remove the tumor and all or part of the surrounding tissue
• Radiation therapy to shrink the tumor before surgery (called neoadjuvant treatment) or get rid of remaining cancer cells after surgery (adjuvant treatment)
• Chemotherapy medication to kill cancer cells throughout your body (can be given before or after surgery)
• Hormone therapy if the tumor is also hormone receptor-positive (helps block hormones that make the cancer grow)
• Immunotherapy to help your immune system find and attack cancer cells
• Targeted therapy to block the specific genes or proteins (like HER2) that help cancer cells grow

Most people with HER2-positive breast cancer receive targeted drug therapy, often combined with surgery, chemotherapy, or radiation. Targeted therapy uses special medications that find and destroy cells that contain the HER2 protein. These drugs block the HER2 receptors, preventing them from sending signals that tell the cancer cells to grow. Without those signals, the cancer cells eventually die.

In recent years, medical research and clinical trials have led to much better outcomes for people with HER2-positive breast cancer. New anti-HER2 treatment options for both early-stage and metastatic breast cancer have dramatically improved survival rates — in some cases, over 90 percent.

The most common HER2-targeted breast cancer therapies are monoclonal antibodies — lab-made proteins that attach to HER2 on cancer cells and help stop them from growing. In 2020, the U.S. Food and Drug Administration (FDA) approved Phesgo, an injectable combination of two monoclonal antibodies (pertuzumab and trastuzumab) and an enzyme (hyaluronidase-zzxf), for treating early-stage or metastatic HER2-positive breast cancer.

Another type of targeted therapy is tyrosine kinase inhibitors (TKIs). TKIs block the HER2 signals that tell cells to grow and divide.

As breast cancer research continues, more targeted treatments and maintenance therapies are becoming available. That means people with HER2-positive breast cancer — and their care teams — have more treatment choices than ever before. If you have questions about your treatment plan or new options for HER2-positive breast cancer, talk with your oncologist (cancer doctor).

Read more about treatments for HER2-positive breast cancer.

Talk With Others Who Understand

MyBCTeam is the social network for people with breast cancer and their loved ones. On MyBCTeam, members come together to ask questions, give advice, and share their stories with others who understand life with breast cancer.

Do you still have questions about the genetics of HER2-positive breast cancer? Share your experience in the comments below, or start a conversation by posting on your Activities page.​