HER-2 Testing Options

The most accurate HER-2 assessment means the most effective therapy decision.

Tests for HER-2 status measure either gene copy number or presence of protein receptors. The two most widely used technologies worldwide and the only two approved by the FDA in the United States are Immunohistochemistry (IHC) and Fluorescence in situ Hybridization (FISH). Chromogenic in situ Hybridization (CISH) and Silver in situ Hybridization (SISH) are two other technologies that measure HER-2 gene copy number. All of these techniques are routinely utilized on formalin-fixed, paraffin-embedded breast tissue.

Fluorescence in situ Hybridization (FISH)
FISH is a cytogenetic technique that can be used to detect and localize the presence or absence of specific DNA sequences on chromosomes. It uses fluorescent probes that can be visualized with a fluorescent microscope.

FISH processfish process

 

 

 

 

 

 

 

 

 

 

FISH for HER-2 is a gene-based test that measures the number of HER-2 genes in a cell. The FISH test "highlights" the HER-2 genes inside the cell, making them appear as fluorescent signals (dots) so they may be accurately counted. PathVysion® FISH also measures the number of copies of chromosome 17 in the cell. Since the HER-2 gene resides on chromosome 17, this adds several measures of control to the test. After counting the HER-2 and Chromosome 17 signals in 20 nuclei, the ratio of HER-2 to Chromosome 17 is calculated. If this value is 2 or greater, the patient is considered amplified for HER-2 or positive. If the test shows a normal gene count, she is considered HER-2 negative. FISH allows the viewer to literally count the genes, making for a more objective assessment. In addition, because this test measures genetic material, which is very stable, tissue preparation has very little effect on test outcome.

pathvysion her-2 dna probe image


















ImmunoHistoChemistry (IHC)
IHC is a technique that utilizes specific antibodies for staining protein in tissues on microscopic glass slides. Immunohistochemical staining is widely used in the diagnosis and treatement of many types of cancer.

The IHC test for HER-2 is a protein-based test that is used to determine the total amount of HER-2 protein receptors on the surface of the cell. The surface of the cell is "stained" with an antibody. IHC is interpreted by the intensity and percentage of cells which exhibit a brown cell surface staining. These specimens are interpreted on a numeric scale of 0 (negative for HER-2 overexpression), 1+ (negative for HER-2 overexpression), 2+ (positive for HER-2 overexpression), and 3+ (positive for HER-2 overexpression).

Issues regarding the accuracy of this method include:

  • The protein may be damaged by the processes of fixing and storing the tissue with  formalin and parrafin, causing variability in test outcome;
  • An assortment of antibodies are used for the testing, including laboratory developed antibodies, which lead to variability; and
  • Interpretation is subjective and requires a great level of skill and expertise.
ihc sample images