The Test Sample
What is being tested?
HER2/neu is short for the human epidermal growth factor receptor 2. It is a gene that is found in healthy cells, but some people with breast cancer have tumors with excess copies of the gene and amounts of the protein it produces. Breast tumors in this category are known as HER2/neu-positive and can be more aggressive and respond differently to treatment than HER2/neu-negative tumors. The HER2/neu test performed on breast tissue determines whether a person's breast cancer is positive for HER2/neu.
In normal cells, the HER2/neu gene codes for a protein that helps promote cell growth. But when a gene mutation results in too many copies in a cell (amplification), HER2/neu then produces too much of the HER2 protein. When this happens, HER2/neu becomes an oncogene, meaning that it can promote uncontrolled, cancerous growth. This only happens in about one in five breast cancers but can also happen in other cancers, such as ovarian and bladder cancer.
Tumors that have this overexpression tend to grow more aggressively and resist endocrine (anti-hormone) therapy and some standard chemotherapies. People with HER2/neu-positive breast cancers tend to have a poorer prognosis, but this tumor characteristic also makes them candidates to receive treatment specific for HER2/neu-positive cancers, also known as targeted therapy.
The American Society of Clinical Oncology (ASCO) and the College of American Pathologists (CAP) jointly recommend that the tumors of all people with invasive or recurrent breast cancer be tested for HER2/neu.
To determine if a tumor is positive for HER2/neu, a biopsy is taken and the sample of tumor is tested. There are two main ways to test HER2/neu status:
- Immunohistochemistry (IHC) measures the amount of HER2 protein present.
- Fluorescent in situ hybridization (FISH) looks at the genetic level for the number of copies of the gene present, known as amplification.
Both IHC and FISH are acceptable testing methods, according to ASCO and CAP. The panel does not express a preference for one over the other. But if one test is indeterminate or negative, then the other should be done as a follow-up test.
Cells shed HER2 protein into the blood and a serum test is available to measure the amount of HER2 protein present in the blood of a person diagnosed with breast cancer. The serum level is loosely associated with the amount of HER2/neu-positive cancer present.
This test is not used for screening purposes and is not a substitute for tissue testing but may be ordered to help assess a person's prognosis and to monitor the effectiveness of treatment.
After an initial diagnosis of metastatic breast cancer is made, this blood test may be performed and if the initial level (baseline) is greater than 15 ng/mL, then the test may be used to monitor treatment. HER2 blood levels that remain high or drop and then increase could indicate that treatment is not working.
How is the sample collected for testing?
NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.
Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.
Is any test preparation needed to ensure the quality of the sample?
No test preparation is needed.