Below this post I have listed several cross-links to articles that address the difference between FISH (Fluorescence In Situ Hybridization)
and IHC (ImmunoHistoChemistry) testing. The FISH and IHC tests are used to determine HER-2 positive status. It should be noted that clinical trials utilizing herceptin generally require FISH testing to confirm HER-2 positive status even if an IHC test was already performed.

I hope this information is helpful.

Warmest regards

Paul C.