There are many types of breast cancer, which vary depending on what causes the cancer cells to grow. Hormone-positive breast cancer uses estrogen and progesterone to fuel the growth of the cancer. HER2-positive breast cancer grows due to an overproduction of a protein called human epidermal growth factor. This protein usually helps to control healthy breast cell growth and production, but in the case of patients who have HER2-positive breast cancer, the protein is overproduced.
If you or someone you love has recently been diagnosed with breast cancer, tests were performed to determine if it is hormone-positive, HER2-positive, or neither. The results of this test determine the best approach for treatment. Some breast cancers don’t have hormone receptors or HER2 receptors; this breast cancer type is called triple-negative breast cancer.
A recent discovery in the diagnosis of breast cancer is a subtype of HER2-positive breast cancer called HER2-low. The tests do not show that it is HER2-positive, but there is evidence of overproduction of the HER2 protein fueling the cancer’s growth.
How is HER2-Low Breast Cancer Defined?
If tests determine that the breast cancer is either hormone receptor-positive or has HER2 overexpression, then your doctor will provide you with an immunohistochemical (IHC) score. This score will share the number of HER2 receptors found, which will place the cancer into one of the following three categories:
- HER2-negative. IHC score is 0 or +1, meaning that an overexpression of HER2 protein was not found
- HER2-positive. An IHC score of 3 or more indicates that HER2 protein fuels cancer cell production.
- HER2-low. An IHC score of +2 means that some overexpression of the HER2 protein is present.
Until recently, patients were either HER2-positive or negative. HER2-low is a category that now includes patients who fall between HER2-positive and HER2-negative. Before, patients who had HER2-low breast cancer were considered HER2-negative and did not receive treatments to slow the growth of the HER2 protein. Clinical research has demonstrated an effective approach for these patients.
How Do HER2 Levels Affect Treatment?
When breast cancer is diagnosed as HER2-positive, a targeted therapy called trastuzumab (brand name: Herceptin®) can be used for patients at almost any stage. HER2-negative patients will not receive this drug.
For those who receive trastuzumab, oncologists will usually recommend additional breast cancer treatments, including surgery, radiation therapy, and/or chemotherapy. If the cancer is HER2-positive and hormone-positive, the patient would most likely also need hormone therapy to slow the cancer’s growth.
In the past, HER2-low patients weren’t given a targeted therapy drug. Now, there is a new, FDA-approved targeted therapy treatment approach that can specifically help patients who have HER2-low breast cancer.
How Does Targeted Therapy Work for Breast Cancer Treatment?
Targeted therapy, also called precision medicine, works by “targeting” specific proteins or mutated genes that cause the growth of cancer cells. For breast cancer, the targeted therapy drugs are usually given through an IV infusion or as an injection.
Targeted therapies cause fewer side effects because the drug only affects the cancer cells.
The targeted therapies for HER2-positive and HER2-low breast cancers are called anti-HER2 therapies. This type of targeted therapy blocks the HER2 receptor proteins in the breast cancer cells so that the protein cannot attach. This causes the cancer growth to slow down and/or stop growing.
Enhertu: A New Treatment Approach for HER2-Low Patients
Thanks to breast cancer research, there is a new drug available for patients with HER2-low breast cancer called Enhertu. The FDA approved Enhertu in August of 2022, so it is a relatively new treatment option. There are three different components of Enhertu, which work to treat breast cancer in several different ways.
- The first component attaches to the HER2 protein to stop the protein from receiving growth signals.
- Another component stops the cells from being able to replicate.
- The final component has a chemotherapy agent that helps the drug bind to the HER2 receptors on the cancer cells.
Who Is Treated with Enhertu?
Enhertu is commonly recommended for patients whose cancer is not operable, such as when the cancer has spread to other parts of the body beyond the breast tissue. To be eligible for Enhertu, you must meet one of the following criteria:
- Having been treated with chemotherapy for metastatic breast cancer
- Received chemotherapy after the surgical removal of breast cancer, and the cancer returned within six months
When determining if you are eligible for Enhertu or deciding on which breast cancer treatment is best for you, your oncologist will consider many factors, including your HER2 status, to determine the most personalized approach.
What to Know Before Taking Enhertu
If your breast cancer specialist decides you are a good candidate for Enhertu, here’s what you can expect.
- How it’s delivered: Enhertu is given through an IV infusion, going directly to the bloodstream through a special IV catheter called a central line or cancer port. This is the same type of infusion device used when giving chemotherapy through an IV infusion.
- Timing of treatment: Every treatment plan will be a little different, but typically, Enhertu is given every three weeks.
- Side effects: Talk with your doctor about any side effects you should expect when taking Enhertu. As with any medication, there are risks of side effects, and you should know what to expect and who to call if you start to have an issue.
Some common side effects of Enhertu include:
- Changes in blood cell numbers
- Increased risk of infection (due to low white blood cell counts)
- Bruising and bleeding (due to low platelet counts)
- Difficulty breathing
- Chest pain
- Nausea and vomiting
- Fatigue
- Hair thinning or hair loss
- Reduced appetite
- Skin rash
- Headache
- Abdominal pain
It is very important to talk with your breast cancer doctor about the potential side effects of Enhertu (or any cancer treatment approach you take) before getting started.
Groundbreaking Breast Cancer Treatment in Hampton Roads & Eastern North Carolina
At Virginia Oncology Associates (VOA), we know the importance of a personalized breast cancer treatment approach. Our oncologists consider the specific type and stage of breast cancer, as well as several other aspects of the patient’s overall health, to develop an effective breast cancer treatment plan. The VOA breast cancer specialists are located in Chesapeake, Hampton, Newport News, Norfolk, Suffolk (Harbour View and Obici), Virginia Beach, Williamsburg, Virginia, and Elizabeth City, North Carolina.
