HER2-positive breast cancers were once considered aggressive and associated with poor outcomes, but effective treatments exist. Doctors use several diagnostic tests to determine if a person has HER2-positive breast cancer.

They start by testing for HER2 gene amplification in tissue samples from a biopsy or surgery. If the results are borderline (called equivocal), doctors may try again using more specialized methods.

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What is HER2?

A gene called HER2 makes a protein that helps breast cells grow, divide and repair themselves. Some cancer cells have extra HER2 protein, which causes them to grow and multiply faster than healthy cells. About one in five invasive (cancer that has spread to other parts of the body) breast cancers are HER2-positive. At the Abramson Cancer Center, we treat HER2-positive breast cancers with medicines that target and destroy cancer cells without harming normal cells.

Doctors test a tissue sample removed during a biopsy if a person has HER2 positive breast cancer. This test is done in a hospital laboratory. HER2 results are available between one and three weeks after the biopsy.

The first test used to detect HER2 is called immunohistochemistry (IHC). It measures how much of the HER2 protein is on the cancer cell’s surface. A score of zero or one is HER2-negative, two is a borderline result, and three means the tumor is HER2-positive. If the IHC score is unclear, doctors may use a more specialized test called fluorescent in situ hybridization (FISH) to check for more copies of the HER2 gene.

Knowing whether breast cancer is HER2-positive is important because it affects treatment options. People with HER2-positive cancers respond better to treatments that target HER2 and kill the cancer cells. The first HER2-directed therapy was Herceptin, and since then, doctors have developed many more medicines that target HER2.

Symptoms of HER2 Positive Breast Cancer

HER2 is a receptor on the surface of breast cells that sends signals for normal cell growth, division and repair. When cancer cells get too many HER2 receptors, they grow and divide too quickly and can spread throughout the body. HER2-positive cancer is more likely to be aggressive than other types of breast cancer, but advances in treatment have improved the outlook for people with this type of cancer.

Doctors determine whether your tumor is HER2 positive using tests called immunohistochemistry (IHC) or fluorescence in situ hybridization (FISH). These tests examine tissue samples from your biopsy. During your examination, a healthcare provider will clean the area where the model will be taken and inject an anesthetic so you won’t feel any pain. The provider will then insert a fine aspiration or core biopsy needle into the site and withdraw a small amount of fluid or tissue for analysis.

The results of these tests tell doctors whether your tumor is HER2 positive or negative and what your prognosis may be. Your doctor can also use the information to determine your best treatments.

Most people with HER2-positive cancer receive the same standard treatments as people with other kinds of breast cancer, such as surgery, radiation and chemotherapy. These treatments can slow or stop the growth of cancer cells and keep them from coming back (recurrence). Some people with HER2-positive cancer may also need drugs that target the HER2 protein, such as trastuzumab (Herceptin). This can increase your chances of getting better results from standard treatments.

Diagnosis of HER2 Positive Breast Cancer

HER2-positive breast cancers tend to grow and spread more quickly than other types of breast cancer. They are more likely to recur and be fatal, but advances in drug therapy over recent years have dramatically improved the outlook for people with this form of breast cancer.

HER2 is normally present on the surface of breast cells and helps them grow and repair themselves. A mutation in the HER2 gene or a buildup of HER2 protein (overexpression) can cause these cancer cells to grow uncontrollably and form a tumor.

The HER2 status of a tumor is determined by an immunohistochemistry (IHC) test, which measures the amount of HER2 protein in the tumor cells. If the IHC score is zero or one, the tumor is HER2-negative. A second test called fluorescence in situ hybridization (FISH) may be performed if the IHC results are borderline or inconclusive.

For most patients, the IHC score and FISH results determine HER2 status. However, if a patient’s HER2 status changes during or after surgery, doctors must retest the tumor and make new treatment recommendations.

Getting a breast cancer diagnosis at a cancer center that routinely evaluates HER2 and treats many people with HER2-positive disease is important. This way, pathologists and oncologists can communicate more easily about the results of HER2 testing and how it might affect treatment options.

Treatment of HER2 Positive Breast Cancer

Once thought aggressive and difficult to treat, HER2-positive breast cancer is more commonly treated than ever. Thanks to ongoing research, doctors have many treatment options for patients with HER2-positive cancer. The cancer stage at diagnosis is an important factor in determining the outcome, as are your age, general health and family history.

Treatment of HER2-positive breast cancer typically involves chemotherapy, radiation therapy, or both. In addition, patients with HER2-positive breast cancer may also receive monoclonal antibody therapy. The antibodies target and block the HER2 receptors on cancer cells to help prevent them from growing. The HER2 inhibitors lapatinib, neratinib and tucatinib are most commonly used to treat HER2-positive cancer. They can cause side effects, such as liver problems and severe diarrhea.

If you have HER2-positive breast cancer, your care team will develop a treatment plan tailored to your unique situation and needs. They will consider the size and grade of the tumor, your hormone receptor (ER) status, and whether or not it has spread to other parts of your body.

Your care team will use a combination of treatments, such as surgery, radiation therapy and chemotherapy, to treat your cancer. They will also recommend other treatment measures, such as hormone therapy or targeted therapies, based on your individual needs and tumor characteristics.