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After a breast cancer diagnosis, there are often more questions than answers. What is the stage and severity? What tests will you need? And what, exactly, will breast cancer mean for your life?
The diagnostic process is often full of uncertainty — especially when test results can take days or even weeks. Still, this process helps your healthcare team personalize your prognosis and treatment recommendations and allows team members to fully address your questions.
You will likely hear your care team talk about testing for your cancer’s HER2 status. HER2 stands for human epithelial growth factor receptor 2, a protein that cancer cells may overproduce. Determining whether your cancer is HER2 positive will help guide important treatment decisions moving forward.
It’s never too early to start the discussion about your cancer’s HER2 status. Below, Tufia C. Haddad, M.D., a breast cancer expert at Mayo Clinic in Rochester, Minnesota, discusses the diagnostic process for HER2-positive breast cancer and why it matters.
What is HER2-positive breast cancer?
Not all breast cancers are the same. In fact, differences in cell type, hormones and protein production mean there are a range of breast cancer types.
Though all breast cancer begins in the same region of the body — the breast — the cancer can originate in a few different types of cells. Whether the cancer starts in the different cells of the milk ducts and lobules or in the glands and connective tissues can impact exactly how the cancer develops and the most effective treatment methods. Similarly, hormones may play a role in how a cancer grows and responds to different treatments. You may hear about hormone receptor status, and this refers to whether the breast cancer cells contain estrogen and progesterone receptors.
Finally, most breast cancers have HER2 protein present on the outside of their cells, but some contain extra copies of the HER2 gene or protein.
For breast cancer, HER2 status can be one of the following:
- HER2 positive. In this situation, the cancer cells have too many copies of the gene or too much of the protein. HER2-positive cancers tend to be more aggressive than HER2-negative cancers, meaning they may grow and spread faster. It’s estimated that about 1 in every 5 breast cancers is HER2 positive. However, Dr. Haddad says that thanks to targeted HER2 treatment, “the pendulum has swung in the direction of a favorable prognosis now.”
- HER2 low. A significant proportion of HER2-negative breast cancers are thought to fall into this category. HER2-low breast cancer indicates that some protein is present on the cancer cells but not enough for the cells to be considered HER2 positive. Depending on your exact test results and protein levels, the cancer may also be considered HER2 ultralow. For a HER2-low or HER-2 ultralow cancer, your care team may discuss targeted therapies.
- HER2 negative. This means the cancer cells are HER2 low or they are not producing any detectable HER2 protein. Compared with HER2-positive breast cancer, HER2-negative and HER2-low cancers tend to grow more slowly.
Keep in mind that these different categories for breast cancer — cell type, hormone receptor and HER2 status — determine your exact diagnosis. For example, the term “triple negative” means the breast cancer is HER2 negative and lacks estrogen and progesterone hormone receptors. Conversely, the term “triple positive” means the cancer is positive for HER2 and estrogen and progesterone receptors. Getting a full picture of these breast cancer characteristics helps your care team create the best treatment plan for your needs.
HER2 breast cancer testing and diagnosis
As a rule of thumb, experts recommend that all invasive breast cancers be tested for HER2.
Dr. Haddad says it’s especially important to advocate for diagnostic testing if there is a cancer recurrence or suspected spreading, known as metastatic disease. “Roughly 15% to 20% of the time, there will be a change in the HER2 status or the estrogen receptor status compared with that of the original tumor,” says Dr. Haddad. As an exception, HER2 testing is not generally done on ductal carcinoma in situ (DCIS), which is a type of noninvasive breast cancer.
There are two types of tests that can determine the HER2 status of breast cancer — an immunohistochemistry (IHC) test and a fluorescence in situ hybridization (FISH) test.
“A pathologist will use the IHC test to identify whether or not the HER2 protein is present on the outside of the tumor cells,” says Dr. Haddad. A HER2 antibody is introduced and, using a microscope, the pathologist can determine if that antibody attaches to the cancer cells.
FISH testing, meanwhile, looks at the HER2 gene that codes for the protein. “In this case, we’re actually looking with FISH to see if there are extra copies of the HER2 gene, which then in turn, would make the extra protein,” says Dr. Haddad.
Neither test is better than the other, according to Dr. Haddad, and the type of test your care team recommends may simply depend on the testing facilities. Many cancer centers opt for IHC due to the faster turnaround time for results. However, the IHC test may indicate that some HER2 protein is present but the results are just below the threshold for a HER2-positive cancer. In this situation, Dr. Haddad says it’s common to test again with FISH to conclusively determine whether the tumor is HER2 negative or positive.
To conduct either IHC or FISH, your care team takes a tissue sample called a biopsy. For most people, Dr. Haddad says an ultrasound-guided biopsy is used, in which a radiologist uses imaging technology to guide a special needle to the tumor site and retrieve a tissue sample. During a biopsy, you’ll usually be awake and given numbing medications to minimize any pain with the procedure.
After analyzing the tissue sample, your care team discusses your pathology report — the documents that describe the results of your biopsy and testing, including your HER2 status. A pathology report can be very technical. Be sure to ask your care team exactly what the report means and don’t be shy about getting clarifications or asking follow-up questions.
Remember, the better you understand your HER2 status, the more active you can be in helping shape the treatment plan that’s right for you and your cancer journey.
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