Whats the difference between IHC and FISH?
• A: IHC and FISH are two different FDA-approved methodologies for assessing HER2 protein overexpression and gene amplification levels, respectively, in biopsy samples. It can be (1) determined directly through immunohistochemistry (IHC), or (2) inferred indirectly through measurement of HER2 gene amplification levels via a method known as fluorescence in situ hybridization (FISH). These tests are quite different in what they detect/measure, how they are scored, and how the results are interpreted. NCCN and ASCO have guidelines for what defines HER2 positivity with respect to IHC and FISH results. • IHC is qualitative; it measures expression of the HER2 protein on the surface of cells. The HER2 protein has been found to be expressed in higher numbers (known as overexpression) in approximately 25% of primary breast cancers. In IHC, the HER2 protein is detected using an antibody against HER2, which in turn is detected with a second labeled antibody. The intensity of cell staining is scor
