HER2-Positive Breast Cancer
You may have heard that between 15 and 20 percent of breast cancers are HER2-positive. But what exactly does that mean?
“HER” is a protein that lives on the outside of breast cells. Some breast cancer cells make too much of this protein, which makes the cells grow faster than normal. This is called HER2-positive breast cancer.
HER2-positive breast cancers can be more aggressive than other types. The good news is that there are effective treatments for this type of breast cancer, called targeted therapies. Other treatments that target HER2-positive breast cancer cells are being tested in clinical trials.
You can get targeted therapy for HER2-positive breast cancer whether you have early-stage or metastatic disease. Sometimes you get the treatment with chemotherapy or other types of medicine. Sometimes you get targeted therapy alone.
The HER2 gene makes HER2 proteins, which act as receptors. They live on the outside of breast cells and receive signals from the body. These signals can tell cells to grow, multiply or repair damage.
Both the HER2 gene and the HER2 protein are part of normal cell growth. They are seen in the breast cells of people who do not have cancer. But sometimes mutations, mistakes in a cell’s DNA, cause the body to make too many HER2 proteins. This can cause breast cells to grow faster than normal, which can lead to breast cancer.
The gene mutations that cause HER2-positive breast cancer are sporadic, meaning they happen at some point during our lives. They are not given to you by your parents or passed on to your children.
After you were diagnosed with breast cancer, you should have had a number of tests to help your doctors learn more about the cancer and how to treat it. You can find your test results in a document called your pathology report.
HER2 tests may include
- The immunohistochemistry (IHC) test, which measures how many HER2 proteins are on the surface of the breast cancer cells.
- The in situ hybridization (ISH) test, which looks for extra copies of HER2 genes in cancer cells. There are two types of ISH tests that use different kinds of microscopes to look at the cancer.
It is possible to have breast cancer that is both HER2-positive and hormone receptor-positive. Cancer that grows because of the hormones estrogen and progesterone, and HER2, is sometimes known as triple-positive breast cancer.
If you have triple-positive breast cancer, your treatment will likely include medicines that target the HER2 receptors and medicines that target the hormone receptors.
Having HER2-positive breast cancer means you will likely take more than one type of treatment at a time. Many researchers are also studying pre-surgery, or neoadjuvant treatment, for HER2-positive early-stage breast cancer.
Targeted Therapies for HER2-Positive Breast CancerTargeted therapies find and attack fast-growing cells that have certain receptors, such as the HER2 receptor. On their own, targeted therapies have far fewer side effects than chemotherapy medicines because they leave cancer-free cells alone. But each targeted therapy has unique side effects that you should discuss with your doctors.
Most targeted therapies are given with chemotherapy because the combination is more effective.
Common targeted therapies for HER2-positive breast cancer are:
Trastuzumab (Herceptin), given by vein and usually with chemotherapy. It attaches to the HER2 proteins and blocks the signals that tell cells to multiply too quickly, causing cancer. Treatment with trastuzumab and chemotherapy cuts the risk of recurrence, or return of the cancer, in half.
Common side effects include fever or chills, muscle aches, nausea, skin reactions at the site of injection, a low white blood cell count and diarrhea. A rare but serious side effect is heart problems.
Pertuzumab (Perjeta), used in early-stage disease when given at the same time as trastuzumab and the chemotherapy medicine docetaxel (Taxotere). Pertuzumab is given by vein as a treatment before surgery, also called neoadjuvant therapy. Like trastuzumab, pertuzumab works by blocking signals that tell breast cancer cells to multiply and grow.
You may be able to take pertuzumab for early-stage HER2-positive breast cancer if the cancer is
- larger than 2 centimeters across.
- locally advanced, meaning it has spread to nearby tissue or lymph nodes.
- inflammatory, a type of breast cancer in the skin of the breast, in which the breast looks red and swollen and feels warm to the touch.
Common side effects include hair loss, diarrhea, nausea, rash, neuropathy and a low white blood cell count. A rare but serious side effect is heart and lung problems.