What is HER-2?
HER2 is a gene that sends control signals to cells in breast tissue, telling them to grow, divide, and make repairs. A healthy breast cell has 2 copies of the HER2 gene. In some cases of breast cancer, the breast cells have more than 2 copies of the HER2 gene, and those copies start over-producing the HER2 protein. As a result, the affected cells grow and divide rapidly, giving rise to cancer.
Positive vs. Negative Test Results. What do they mean?
When breast cancer cells are tested for HER2 status, the results are reported as either positive or negative. If the results are HER2 positive, it means the HER2 genes are over-producing the HER2 protein, and that those cells are growing rapidly and creating the cancer. If the results are HER2 negative, then the HER2 protein is not causing the cancer.
Why is it important to know HER2 status?
There are two reasons to know the HER2 status in cases of breast cancer:
- HER2 positive tumors tend to grow more aggressively than HER2 negative tumors.
- HER2 positive tumors can be treated by Herceptin (Trastazumab), which is a drug that targets the HER2 protein
production and can help to stop the growth of HER2 positive tumor cells.
Therefore, by knowing the HER2 status of the cancer cells, the oncologist can choose the right medication/chemotherapy for the patient.
What are the tests for HER2 status:
Immunohistochemistry (IHC)
this test measures the production of the HER2 protein by the tumor. The test results are ranked as 0, 1+, 2+, or 3+. If the results are 2 + or 3+, the cancer is HER2-positive.
Fluorescence In Situ Hybridization (FISH)
this test uses fluorescent probes to look at the number of HER2 gene copies in a tumor cell. Tumor cells with Her2 gene amplification show increased copies of the Her2 gene signal (orange) as compared to the Chromosome 17 centromere signal (green).
The FISH test is more sensitive than immunohistochemistry, and a lot of cases previously tested by IHC are confirmed by FISH testing.