• The genetic changes found in your breast tumor influence your prognosis and help your care team recommend the most effective treatment combination.
• Breast cancer cells that are HER2-positive contain high levels of HER2, a protein that encourages cell growth.
• HER2-positive breast cancer cells tend to grow and spread quickly, but newer treatments such as targeted therapies are improving life expectancy.

Cancer begins when the genes in a cell develop certain types of mutations. Knowing which mutations your breast cancer cells carry will help you and the rest of your cancer care team understand your condition better.

About 20 percent of all breast cancer cases are HER2-positive. Most breast cancers are HER2-negative, although researchers are also recognizing a newer category, HER2-low.

HER2 status is one of many factors of breast cancer that describe important characteristics of tumors and help predict how they will grow. Your care team can more accurately forecast your prognosis (predicted outlook) and the treatments that are most likely to be successful when they are aware that your cancer is HER2-positive (also written as HER2+).

The HER2 Gene

Genes often have very long, specific names. The full name of the HER2 gene is human epidermal growth factor receptor 2. This is often shortened to HER2 receptor, HER2/neu, or simply HER2. It also sometimes goes by other names, such as ERBB2.

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

In HER2-positive breast cancer, cell damage results in gene amplification, in which many extra copies of the HER2 gene are made. 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. Knowing your cancer is HER2-positive helps doctors understand why your cells are growing abnormally and provides insights about how to treat the tumor.

“Is HER2 Genetic?”

Genetic mutations can be either acquired over time or genetic (inherited from parents). Most cancer is a result of acquired mutations that develop throughout life. In the case of HER2, the mutation is not passed down from parent to child. It’s believed to develop over time as an acquired mutation and may be influenced by environment and lifestyle.

Testing for HER2

If you are diagnosed with breast cancer, your care team will probably recommend you go through genetic testing to determine your HER2 status. This testing can be performed on your biopsy tissue or through a blood test. Genetic tests can also help your doctor see whether your cells have other cancer-related proteins, such as hormone receptors.

The first step of breast cancer diagnosis and HER2 testing is often getting a biopsy. During this procedure, doctors remove a sample of your breast tissue. The sample will then be examined using tests such as:

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

Together, these tests provide genomic information about your breast cancer cells and create a picture of your hormone receptor status. Read more about diagnostic tests for HER2-positive breast cancer.

Treatments for HER2-Positive Breast Cancer

Individuals with all subtypes of breast cancer may need treatments like:

• Surgery to remove the tumor and all or part of the surrounding breast
• Radiation therapy to get rid of remaining cancer cells after surgery (called adjuvant treatment) or shrink the tumor before surgery (neoadjuvant treatment)
• Chemotherapy medication to kill cancer cells throughout the body, which can be administered before or after surgery
• Hormone therapy, if the tumor is also hormone receptor-positive

Most people with HER2-positive breast cancer will receive targeted therapy. These medications can find and destroy any cell that contains HER2 protein. Targeted therapy drugs attach to HER2, preventing it from sending signals to the cell to tell it to continue growing. This eventually leads to death of the cell.

Clinical trials are underway to develop new anti-HER2 treatment options, both for early-stage and metastatic (cancer that has spread) breast cancer.

Read more about treatments for HER2-positive breast cancer.

How Does HER2 Affect Your Life Expectancy?

Breast cancers that are HER2-positive tend to grow more quickly than HER2-negative breast cancers. In the past, individuals with HER2-positive breast cancer often didn’t have a good prognosis for survival. However, newer cancer treatments have helped many people with HER2-positive cancer have better outcomes. When using modern treatment plans, individuals with HER2-positive breast cancer have better survival rates. More than 3 out of 4 people with HER2-positive breast cancer live for more than 10 years after their diagnosis.​

Sometimes, after cancer is treated the first time, it can come back. This is known as a relapse. Targeted treatments for HER2-positive breast cancer help lower the risk of relapse.

Other factors may increase or decrease this risk of relapse, however. If the tumor is large or has spread beyond the breast, cancer may be more likely to come back. On the other hand, individuals with tumors that are both HER2-positive and hormone receptor-positive may have a lower risk of relapse.

Talk With Others Who Understand

MyBCTeam is the social network for people with breast cancer and their loved ones. On MyBCTeam, more than 61,000 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 or how they affect life expectancy? Share your experience in the comments below, or start a conversation by posting on your Activities page.​