There are primarily two methods for HER2 testing: Immunohistochemistry (IHC) and Fluorescence In Situ Hybridization (FISH).
- IHC: This test measures the amount of HER2 protein on the surface of cells in a cancer tissue sample. The results are scored from 0 to 3+, with 0 and 1+ considered HER2-negative, 2+ as equivocal, and 3+ as HER2-positive. - FISH: This test looks for HER2 gene amplification in the cancer cells. It uses fluorescent dyes to highlight the HER2 genes. A positive FISH test indicates HER2 gene amplification.
In cases where the IHC results are equivocal (2+), FISH testing is often used as a follow-up to confirm the HER2 status.
