Benchmarking a large regional UK HER2 testing service against current practice guidelines.

Aims: To critically evaluate HER2 testing data for 3500 consecutive cases over 28 months for a single laboratory and review these findings in the light of current UK reporting guidelines.

Methods: We have reviewed all data relating to the HER2 testing service including reagents and analytical machine, HER2 immunohistochemistry (IHC) and fluorescent hybridisation (FISH) scoring profiles. We have examined the place of double counting and rapid screening of FISH and when it is and is not safe to do so.