local vs central Her2 testing?

"Initial findings from the Breast Cancer Intergroup study N9831 of adjuvant trastuzumab indicated that only 74% of cases found to be HER2+ upon local testing (IHC 3+ or FISH+) were confirmed to be positive on central testing.18 This trial was subsequently amended to require central confirmation of HER2+ status, and over time, a higher level of concordance between local and central testing has been seen. Currently, when local and central evaluations used the same methodology, concordance is 87.0% for FISH and 81% for the HercepTest™.19 It is interesting that among cases tested locally by FISH, 13% were still not confirmed on central FISH testing."

Anyone know what the difference between local and central testing is and which is done more commonly?