Breast Cancer HER2 Testing: What You Need to Know

Breast Cancer HER2 Testing is an important part of breast cancer diagnosis and treatment. Learn what it is, why it’s done, and what the results mean.

By Dr. Heba hegzy On Apr 6, 2023

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Breast Cancer HER2 Testing is a crucial step in the diagnosis and treatment of breast cancer. This test helps determine if a patient’s cancer cells have an excess of HER2 protein, which can affect the aggressiveness of cancer and the effectiveness of certain treatments. In this guide, we’ll explore what HER2 testing is, why it’s done, and what the results mean for breast cancer patients.

What is Breast Cancer HER2 Testing?

HER2 is proteins found on breast cancer cells, So HER2 testing is a crucial component in the diagnosis and treatment of breast cancer. This test helps determine if breast cancer cells are producing an abundance of HER2 proteins, which can lead to more aggressive cancer growth. By analyzing a tissue sample from a biopsy, doctors can determine the HER2 status of the breast cancer.

HER2-positive breast cancer is a specific subtype of breast cancer posing unique treatment challenges. HER2 testing is essential to developing appropriate treatment plans for patients diagnosed with this subtype of breast cancer. Understanding the purpose of HER2 testing is a critical element in providing effective and individualized care to patients with breast cancer.

To determine HER2 status in breast tumors, doctors use one of two diagnostic tests: immunohistochemistry (IHC) or fluorescence in situ hybridization (FISH). During an IHC test, a sample of tumor tissue is analyzed to measure the amount of HER2 on the surface of the cell. A score of zero or one indicates a negative test result, and a score of three is considered positive. Scores of two are inconclusive and may require further testing.

FISH testing looks at the genetic material of the tumor cells to determine whether there are extra copies of the HER2 gene. In cases where IHC results are ambiguous or borderline, FISH testing is often used for confirmation. HER2 testing is a critical component in determining appropriate breast cancer treatment options.

There are several alternative terms that refer to the same concept, such as: human epidermal growth factor receptor 2, ERBB2 amplification, HER2 overexpression, and HER2/neu tests.

What is the difference between IHC and FISH tests?

HER2 amplification testing is an essential tool for assessing breast cancers. The two primary methods used are immunohistochemistry (IHC) and fluorescence in situ hybridization (FISH). The IHC test measures protein expression, while the FISH test measures the gene copy number. IHC is a faster and more cost-effective method, but FISH is considered more reliable. IHC can produce equivocal results, which require further testing with FISH for confirmation. The criteria for considering a tumor HER2-positive vary depending on the method used. A tumor is deemed HER2-positive if the IHC result is 3 or the FISH result is above the defined cut-off value. HER2 status plays a crucial role in deciding the treatment regimen for breast cancer patients. HER2-targeted therapies are associated with potential side effects, including heart problems, but these can be monitored through regular medical check-ups. In summary, both IHC and FISH tests are essential tools for assessing HER2 status in breast cancer, and their differences lie primarily in their mechanisms of testing and reliability.

What is Breast Cancer HER2 Testing used for?

In case you have been diagnosed with breast cancer, this examination might be required to determine whether your cancer is HER2-positive or HER2-negative.

Additionally, it may be utilized occasionally to determine your therapy’s effectiveness by checking the levels of HER2. If the levels are normal, it indicates a positive response to treatment; whereas high levels suggest that the treatment is ineffective or cancer has returned following treatment.

Process of a HER2 breast cancer examination

To test for HER2 marker, a biopsy is usually performed by taking a sample of the tumor tissue. There are three primary methods of performing a biopsy:

Core needle biopsy, This method involves the use of a bigger needle to extract a specimen.
Fine needle aspiration biopsy (FNA), A technique is utilized where a needle, which is very thin in size, is employed to extract a sample of either breast cells or fluid.
A surgical biopsy, A small and simple medical procedure is carried out to extract a sample. This procedure does not require the patient to be admitted to the hospital and can be done on an outpatient basis

In FNA and core biopsies

The typical process generally consists of these stages:

The biopsy area will be sanitized by a medical professional and given an injection of anesthesia to eliminate any discomfort during the process.
After numbing the region, the healthcare practitioner will introduce a slender aspiration needle or a core biopsy needle into the biopsy area to get a tissue or fluid sample.
You might experience slight discomfort during the withdrawal of the sample.
The biopsy site will be subjected to pressure until the bleeding ceases.
At the site where the biopsy is performed, your healthcare provider will place a clean and germ-free bandage.

In a surgical biopsy

To extract all or a portion of a lump in the breast, a surgeon will make a minor incision into your skin. If the lump cannot be accessed through needle biopsy, surgical biopsy is performed. Typically, surgical biopsies consist of these steps:

You could receive a sedative medication to induce relaxation.
Either local or general anesthesia will be administered to ensure you do not experience any pain while undergoing the procedure
To provide local anesthesia, a medical practitioner will administer medication through injection to the biopsy location in order to render it numb.
After the biopsy site is numbed or if you are under anesthesia, a small incision will be made by the surgeon in the breast to extract some or all of the lump. There might be a removal of other tissue located around the lump as well.
Either stitches or adhesive strips will be used to close the wound on your skin.

The biopsy method chosen depends on various factors such as the tumor’s size and location. Although HER2 measurement in blood tests is possible, it has not been found to be beneficial for a majority of patients. Therefore, it is typically not advised.

After obtaining the sample from the tumor, it is preserved in a 10% formalin solution, then it is sent to the pathology laboratory, then it is passed in several steps until it reaches a paraffin block through which slices are made and then inserted into the immune markers device to perform the HER2 test, which appears on the slide with a brown stain, while the other parts staining with blue, Finally it is diagnosed by pathologists.

Preparation for the test

If you only receive local anesthesia for the biopsy site, there is no need to make any special arrangements. However, if you are getting general anesthesia, it may be necessary to refrain from eating or drinking for a certain period of time before the procedure. The surgeon will provide more detailed guidance on this matter., If you receive a sedative or general anesthesia, it is important to organize transportation for yourself as you may feel disoriented and drowsy after the process.

“Related: CA-125 blood test, Preparations and Results interpertations“

Risks to the test

After a biopsy, you could experience minor bruising or bleeding in the area. In some cases, the site may become infected and require treatment with antibiotics. Surgical biopsies may also result in additional pain and discomfort, for which your healthcare provider may suggest medication to ease symptoms.

“Related: CA 19-9 Blood Test, What Is It? How Does it Work?“

Results interpretation

When HER2 protein levels are elevated, or additional copies of the HER2 gene are discovered, it is likely an indication of having HER2-positive cancer. Conversely, if the results indicate standard quantities of HER2 protein or average numbers of HER2 genes, then one probably has HER2-negative cancer.

If your test results were inconclusive, it is likely that you will undergo another test. This may involve using a different tumor sample or testing method. Typically, the first test done is IHC which checks for the HER2 protein. If this does not give clear results, FISH can be used to check for extra copies of the gene. While IHC testing is less expensive and quicker than FISH, it may not always give conclusive results.However, the majority of experts in breast health believe that FISH testing provides a higher level of precision.

HER2-positive breast cancer can be considerably reduced in size by treatment, and usually without significant negative effects. However, such treatments are not useful for HER2-negative cancers.

If you are undergoing treatment for cancer with an excess of HER2, a normal outcome can imply that the treatment is working effectively. On the other hand, results indicating higher than average levels could indicate treatment failure or the return of cancer post-treatment.

How is HER2 status used in breast cancer treatment?

Once the HER2 status of a breast cancer patient has been determined, doctors can use this information to determine the best course of treatment. HER2-positive breast cancer typically responds well to targeted therapies, such as trastuzumab (Herceptin), which specifically target the HER2 protein. These targeted therapies can be used in combination with chemotherapy to increase the chances of successful treatment. On the other hand, HER2-negative breast cancer typically responds better to other types of treatment, such as hormone therapy. By accurately identifying the HER2 status of a patient’s cancer, doctors can tailor their treatment plan to be more effective and increase the chances of a positive outcome.

Is this test only for women?

Breast cancer, which includes HER2-positive breast cancer, is prevalent in women but can also impact men. If a man has received a diagnosis of breast cancer, it may be necessary for them to undergo Breast Cancer HER2 Testing.

Moreover, individuals of both genders may require examination for HER2 if they have been detected with specific types of stomach and esophageal cancers.In some cases, these types of cancers exhibit elevated amounts of the HER2 protein and may show positive results when treated with cancer therapies targeting HER2-positive cells.

The use of Breast Cancer HER2 Testing in breast cancer treatment has revolutionized the way doctors approach the disease, greatly improving the chances of successful treatment and recovery.