There are two FDA-approved commercial kits available for HER2 IHC; Dako HercepTest and Ventana Pathway. These are highly standardised, semi-quantitative assays which stratify expression levels into; 0 (<20,000 receptors per cell, no visible expression), 1+ (~100,000 receptors per cell, partial membrane staining, < 10% of cells overexpressing HER-2), 2+ (~500,000 receptors per cell, light to moderate complete membrane staining, > 10% of cells overexpressing HER-2), and 3+ (~2,000,000 receptors per cell, strong complete membrane staining, > 10% of cells overexpressing HER-2). The presence of cytoplasmic expression is disregarded. Treatment with trastuzumab is indicated in cases where HER2 expression has a score of 3+. However, IHC has been shown to have numerous limitations, both technical and interpretative, which have been found to impact on the reproducibility and accuracy of results, especially when compared with ISH methodologies. It is also true, however, that some reports have stated that IHC provides excellent correlation between gene copy number and protein expression.