Types of HER-2 Testing
Tests for determining HER-2 status measure either gene copy number or protein. The two most widely used types of tests are ImmunoHistoChemistry (IHC) and Fluorescence in situ Hybridization (FISH). The PathVysion test employs FISH technology to determine HER-2 status.
The IHC test is a protein-based test that is used to determine the total amount of HER-2 protein receptors on the surface of the cell. To do this, the surface of the cell is "stained" with an antibody. The surface protein measured by IHC can be damaged during preparation of the tissue sample and this may cause variability in outcome. A pathologist must judge the degree of color change in the cell to determine a HER-2 protein measurement level of 0, 1+, 2+, or 3+. Because this test is subjective, the results often are confirmed by performing a FISH test.
FISH 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 fluorescent so they may be accurately counted. If a patient has more than two genes per cell, she is considered HER-2 positive. If the test shows a normal gene count, the test results are considered HER-2 negative. FISH allows the physician or pathologist to literally count the genes, allowing for a more objective assessment of test results and helping to positively identify women who are candidates for HER-2-targeted therapies.
