There are different methodologies of determining the ERBB2 status in breast cancer. Immunohistochemistry (IHC) and fluorescence in situ hybridization (FISH) are two FDA-approved technologies for the detection of ERBB2 amplification. The former detects overexpression of the ERBB2 receptor on the cell membrane while the latter detects the copy number of the gene itself relative to the chromosome 17 centromere.