HER-2 is a gene that controls the production of special proteins called HER-2 receptors on the surface of breast cells and ovarian cells.
Approximately 25% to 30% of breast cancer cells have extra copies of the HER-2 gene, which results in extra amounts of the HER-2 receptors on the surface of the breast cancer cells. If a breast cancer cell over-expresses (i.e., makes too many) HER-2 receptors, these breast cancers tend to grow very quickly and have a tendency to spread.
The growth of HER-2 breast cancers can be slowed by a treatment called Herceptin, which is anti-HER-2 antibody therapy.
There are two tests used to determine whether or not the cancer cell has too much HER-2:
ICH (ImmunoChemistryHistology) Test, which determines if there is too much HER-2 receptor protein on the surface of the breast cancer cell. Results range from 0 (negative), 1+ (negative), 2+ (borderline) to 3+ (positive).
FISH (Fluorescence In Situ Hybridization) Test, which determines if there are extra copies of the HER-2 gene inside the breast cancer cells. FISH results are either positive, meaning that the breast cancer cells have extra copies of the HER-2 gene; or negative, indicating that the breast cancer cells have a normal number of copies of the HER-2 gene.