Receiving a HER2-positive breast cancer diagnosis can be life-changing. You may wonder how a HER2-positive diagnosis will affect your prognosis (outlook) and life expectancy.

Human epidermal growth factor receptor 2, or HER2, is a gene involved in a certain type of breast cancer. In the past, HER2-positive breast cancer was more difficult to treat, and more people died from the condition. However, over the past 30 years, new treatments have dramatically improved the outlook for people with HER2-positive breast cancer.

Read on for more information about the current state of HER2-positive breast cancer prognosis.

What Is HER2-Positive Breast Cancer?

Between 15 percent and 20 percent of all breast cancers are considered HER2-positive, according to the American Cancer Society. The HER2 gene tells your cells to make the HER2 protein. HER2 is a type of protein called a tyrosine kinase receptor — it sits both inside and outside a cell.

When the HER2 protein is activated, it binds to similar proteins, which triggers signaling inside the cell that eventually leads to cell growth and replication. Cell replication is the process of new cells replacing dying, unhealthy cells. When too many cells form before others die, a buildup of cells can result.

If your body has too much of the HER2 gene or protein, known as HER2 overexpression, your cells grow and replicate faster than normal. HER2-positive breast cancer is a type of breast cancer that has too much HER2 protein in the cells of the tumor.

Doctors can test for the amount of HER2 protein in your tumor by taking a biopsy, or sample, of the cancerous breast tissue. They can then perform immunohistochemistry (IHC) to look for the HER2 protein. Some tests look at the amount of HER2 gene in your tumor cells.

IHC tests can tell you your HER2 status, which ranges from zero to 3. A HER2 status of 3 means you’re HER2-positive, and your cancer will likely respond to HER2-positive treatment.

How Does HER2 Affect Life Expectancy?

HER2-positive breast cancers tend to grow faster 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 lead to better outcomes.

When following 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 more than 10 years after their diagnosis.​

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

Understanding HER2-Positive Breast Cancer Survival Rates

When doctors describe survival rates for cancer, they’re usually referring to the five-year survival rate. This statistic estimates the number of people diagnosed with a type of cancer who are still alive five years after their diagnosis. If a specific cancer has an 80 percent five-year survival rate, this means that 80 percent of people were alive five years after their diagnosis.

Doctors may also talk about relative survival rates. These, too, are usually taken at five years, but these rates compare the percentage of people with cancer to a population of same-aged individuals without cancer. An 80 percent five-year relative survival rate would mean that five years after their diagnosis, people with a type of cancer are 80 percent as likely to be alive as their cancer-free peers.

Factors Influencing Prognosis of HER2-Positive Breast Cancer

People with HER2-positive breast cancer have different survival rates than those with HER2-negative breast cancer. Breast cancer survival rates depend on many different factors, including:

• Cancer location, or how much the cancer has spread (known as metastasis)
• Breast cancer subtypes
• Treatment approach
• Individual characteristics, like age and overall health

It’s important to remember that survival rates are averages of the entire population. Your prognosis will depend on your unique set of circumstances and risk factors.

Cancer Location

One way doctors estimate prognosis is based on where your cancerous tumors are located. Tumors can be described as:

• Localized — Only in your breast tissue
• Regional — In tissues close to your breast
• Distant — In breast tissue and other tissues around your body (metastatic breast cancer)

For HER2-positive breast cancer, five-year survival rates are 100 percent for localized cancers, 90 percent for regional cancer, and 32 percent for distant cancers.

Breast Cancer Subtypes

Breast cancer can also be positive or negative for a type of protein called hormone receptor (HR). Some breast cancers have more receptors that respond to hormones like estrogen or progesterone. Your receptor status describes which proteins are abundant in your cancer.

The five-year relative survival rate for HER2-positive, HR-positive breast cancer is 91.5 percent. The five-year relative survival rate for HER2-positive, HR-negative breast cancer is 87.5 percent.

Treatments for HER2-Positive Breast Cancer

There are many treatment options for HER2-positive breast cancer. Because it has higher levels of HER2 proteins than HER2-negative breast cancer, HER2-positive breast cancer calls for specific treatments. Medications aim to reduce the amount of HER2 protein by blocking it from allowing cell growth and replication. These drugs are especially effective when given in the early stages of cancer.

Many HER2-specific treatments work with the immune system to help fight off cancer cells in an approach called immunotherapy. Your body makes proteins called antibodies to block foreign invaders, like viruses, and signal the immune system to destroy potential invaders.

Monoclonal antibodies are a type of immunotherapy used to treat HER2-positive breast cancer. These antibodies are like the ones our bodies make, but they block the HER2 protein. Common monoclonal antibody therapies for HER2-positive breast cancer include:

• Margetuximab-cmkb (Margenza)
• Pertuzumab (Perjeta)
• Trastuzumab (Herceptin)

Although these treatments are usually given through IV infusion in a clinic, pertuzumab and trastuzumab are now combined in a medication called Phesgo that can be administered at home by a health care professional.

Some drugs stop the signaling pathways that happen when tyrosine kinase receptors (like HER2) are active. These include:

• Lapatinib (Tykerb)
• Neratinib (Nerlynx)
• Tucatinib (Tukysa)

Antibody-drug conjugates also are available for HER2-positive breast cancer. These treatments have a monoclonal antibody attached to a drug.

Many targeted therapies for HER2-positive breast cancer are given with chemotherapy, radiation therapy, or surgery. Depending on the type of breast cancer treatment, these therapies may be more effective before, during, or after other treatments.

New Research on HER2-Positive Breast Cancer Treatments

Research for improving treatments for HER2-positive breast cancer is growing. For example, drug companies are developing new antibody-drug conjugates and tyrosine kinase inhibitors, which block tyrosine kinases.

More than 500 clinical trials are focusing on HER2-positive breast cancer. These trials are testing new treatments to find which ones work best for different cancer stages. The goal is to keep improving the prognosis for people living with 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, more than 70,000 members come together to ask questions, give advice, and share their stories with others who understand life with breast cancer.

Do you have HER2-positive breast cancer? Do you have more questions about the prognosis and life expectancy of HER2-positive breast cancer? Share your experiences in the comments below, or start a conversation by posting on your Activities page.