OBJECTIVETo retrospectively evaluate the HER2 status of 1 501 invasive breast cancer (IBC) by immunohistochemistry (IHC) and fluorescent in situ hybridizaion (FISH), and to compare and analyze the changes and their effects, using the 2007 and 2013 American Society of Clinical Oncology/College of American Pathologist(ASCO/CAP) HER2 testing guidelines.

METHODSTissue handling and HER2 testing were performed according the 2007 ASCO/CAP guideline recommendations. The HER2 status of all newly diagnosed IBC were routinely assessed by IHC, and reflex FISH assay was done on all the IHC equivocal (IHC 2+) cases. The HER2 status of 1 501 cases of IBC was re-evaluated according to these two criteria.

RESULTSUsing the 2007 and 2013 ASCO/CAP criteria, the overall positive, equivocal and negative rates of HER2 over-expression and/or amplification in the 1 501 IBCs were 23.05% and 23.52%, 11.59% and 12.52%, and 65.36% and 63.96%, respectively. The positive and equivocal rates increased by 0.47% and 0.93% respectively, but the negative rate decreased by 1.40% when using the new criteria. For HER2 IHC staining using the 2007 and 2013 guidelines, the positive, equivocal and negative rates were 17.99% and 18.13% (+0.13%), 32.51% and 32.91% (+0.40%) and 49.50% and 48, 97% (-0.53%), respectively. FISH for HER2 amplification was done in 348 of the 1 501 IBCs, and using the 2007 and 2013 guidelines, the positive, equivocal and negative rates were 27.59% and 29.02% (+1.43%), 1.15% and 3.74% (+2.59%) and 71.26% and 67.24% (-4.02%), respectively.

CONCLUSIONSThe application of 2013 ASCO/CAP guideline could lead to an increase in positive and equivocal rates, and a decrease in negative rate. The influence could be more prominent for the evaluation of FISH result, and would raise the positive and equivocal rates since a mean HER2 copy number is used in the new criteria. Our re-estimation of IHC result was concordant with the prediction of the guideline.