Despite developments of specific molecular markers, immunohistochemistry staining remains a vital component of laboratory testing for the demonstration of gene amplification.
- Patients with 0 to 1+ IHC staining are more than likely negative for HER2 gene amplification
- Patients with 3+ IHC staining are more than likely positive for HER2 gene amplification
The benefits of IHC staining include low cost and rapid turnaround time.
Patients with 2+ IHC staining are not reliably negative or positive for HER2 gene amplification. Therefore, Fluorescence in Situ Hybridization (FISH) testing must be performed for gene enumeration in 2+ cases. In 3% of cases, protein expression does not correlate with gene amplification.
The primary benefit of FISH testing is accuracy. Drawbacks of FISH methods include high complexity of test performance, high cost of the test, storage/archival over any extended amount of time causes loss of signal and slides are interpretable, and need for a specialized microscope.
