Human epidermal growth factor receptor (HER2) protein exists in the breast tissue and helps control the production of healthy breast cells. Early in the breast cancer diagnosis process, tests are run to see if there is an overgrowth of this protein caused by a mutation in the HER2 gene. The results help direct the treatments recommended by the cancer specialist.
What is HER2-Low Breast Cancer?
HER2 molecules are measured using an immunohistochemical score or IHC score. After the test is run for HER2 protein receptors, the patient is assigned one of the following results:
- HER2-negative - If your IHC score for HER2 levels comes back at 0 or +1, then your breast cancer is considered HER2-negative.
- HER2-positive- If you have an IHC score of 3 or more the breast cancer cells have a lot of HER2 protein receptors present on the surface.
- HER2-low - This is a recently developed category of breast cancer with a borderline IHC score of 2+. While not enough protein receptors were found to consider the cancer HER2 positive, it’s also not HER2 negative.
In the past, HER2-low breast cancers would be classified as being HER2-negative, even though they still express low levels of the protein. Remarkably, about 55% of breast cancers are considered HER2-low.
How Does HER2 Status Affect the Treatments Used?
The IHC test is performed to determine HER2 status because the results of the test affect which treatments are likely to work best. Armed with this information along with other test results such as hormone status tests, the breast cancer doctor is able to make better decisions about which treatments are likely to be most effective.
HER2-positive breast cancers are likely to respond well to a targeted therapy called trastuzumab, with a brand and name of Herceptin (among others). Other treatments are likely to be used before and/or after surgery such as chemotherapy, radiation therapy and hormone therapy depending on the stage of cancer. The targeted therapy uniquely directs itself towards the HER2 receptors to block the reproduction of those cells.
In the past, HER2-low patients weren’t typically given an opportunity to use the most effective HER2 targeted therapy drugs to treat their breast cancer. They would be treated as though they were HER2-negative. Today they’re given the opportunity, if specific circumstances are present, to use the latest in breast cancer treatment drugs approved by the FDA for HER2-low breast cancer.
HER2-negative patients will receive other treatments based on their other test results for estrogen or progesterone hormone receptors which can cause breast cancer to grow. In some cases, the breast cancer is considered triple-negative which means it isn’t being fueled by an overgrowth of the HER2 protein, estrogen or progesterone. For these patients, a different treatment path is suggested.
How Do Targeted Therapies Treat Breast Cancer?
Targeted therapy uses medications that specifically attack cancer cells while leaving the other healthy cells alone. This type of cancer treatment is beneficial since it causes less damage to the healthy cells that surround a tumor.
Targeted therapies vary depending on the type of cancer they're treating. Different types of targeted therapy chemotherapy drugs work differently to attack cancer cells. They may work by:
- Helping the immune system destroy cancer cells
- Interrupting cancer cell growth signals
- Stopping signals that help form blood vessels
- Delivering substances that kill cancer cells
- Causing cancer cells to die
- Starving cancer cells of the hormones they need to grow
Targeted therapies for HER-2 positive and HER-2 low breast cancers are known as anti-HER2 therapies. Anti-HER2 therapies work by attaching to the HER2 receptor proteins in breast cancer cells. The drugs block the HER2 receptors from receiving growth signals, slowing or stopping the growth of cancer. Anti-HER2 therapies are specifically for either HER2-positive breast cancer or HER2-low breast cancer, not HER2-negative breast cancer.
Enhurtu: New Hope for HER2-low Patients
HER2-low breast cancer has recently become treatable with an FDA-approved drug called Enhertu. In fact, FDA approval was given on August 5, 2022. This medication is specifically designed to treat HER2-low breast cancers that are metastatic and that are not surgically removable.
Enhertu has three different parts that work on cancer in different ways.
- One component of Enhertu attaches to the HER2 protein to stop it from getting growth signals.
- Another component interferes with the cell's ability to replicate.
- The third part of the drug contains a chemotherapy agent that helps the targeted therapy drug bind to the HER2 receptors on the cells.
Who is Eligible for Treatment with Enhertu?
To be eligible for treatment with Enhertu, you must have HER2-low breast cancer that cannot be removed surgically or has metastasized (spread to other areas of the body).
Patients must also have been previously treated with chemotherapy for metastatic breast cancer or given chemotherapy following surgical removal and had the cancer return within six months.
The skilled physicians at Rocky Mountain Breast Specialists will consider your entire health history when determining what type of cancer treatment is ideal.
What to Expect When Taking Enhertu
If your doctor decides you're a good candidate for treatment with Enhertu, you can expect to receive the medication through an IV infusion. This medication administration is delivered directly to your bloodstream and will utilize a specialized type of IV called a central line or cancer port.
Enhertu is usually given every three weeks, but treatment plans may vary.
The Latest Treatments Available to Breast Cancer Patients in Colorado
At Rocky Mountain Breast Specialists, we’re happy to offer this new, breakthrough treatment to our breast cancer patients who qualify.
Request an appointment at one of our locations throughout Colorado with a breast cancer specialist who can review test results and talk to you about the next best steps.