HER2 Testing: How To Get High Concordance Rate between Immunohistochemistry and Fluorescence In Situ Hybridization
T Khoury, Y Zakharia, H Hwang, W Liu, S Edge, D Tan, C Morrison. Roswell Park Cancer Institute, Buffalo; Unity Hospital, Rochester; MD-Anderson Cancer Center, Houston
Background: ASCO-CAP 2007 has expanded the equivocal HER2 by immunohistochemistry (IHC) to include cases that have intense complete staining in <30% of tumor cells instead of <10%. The purpose of this study was to find how a high concordance rate between IHC and fluorescence in situ hybridization (FISH) can be achieved.
Design: A series of 452 breast cancer cases were retrieved from our files from 2007 to 2009. All cases were tested for HER2 (DAKO rabbit polyclonal antibody A805). 2+ category was expanded to include cases that had intense complete circumferential staining in <90% instead of ASCO-CAP's criteria of <30% and incomplete weak or non-uniform staining in >10% which would have been designated as 1+ by ASCO-CAP. These cases were tested by FISH (pathVysion, Vysis). FISH results were scored as not amplified, equivocal or amplified when the HER2/Cep17 ratio was < 1.8, 1.8-2.2, or > 2.2, respectively. In addition, HER2 FISH was performed on 40 cases of 3+ and 61 cases of 0 or 1+ that were randomly selected.
Results: Using our criteria, there were 51 (11.3%) 3+ cases, 185 (40.9%) 2+ cases, 72 (15.9%) 1+ cases and 144 (31.9%) 0+ cases. Using ASCO-CAP criteria, there were 72 (15.9%) 3+ cases, 133 (29.4%) 2+ cases, 103 (22.8%) 1+ cases and 144 (31.9%) 0+ cases. Therefore, there were 52 (11.5% of total) additional cases that were reclassified as 2+ (31 from 1+ and 21 cases from 3+). FISH results on the additional 52 cases are illustrated in [table]. While, this expansion on the lower end of the spectrum (1+ category) identified 1 case with HER2 amplification, the expansion on the higher end (3+ category) identified 3 cases with borderline HER2 and 7 cases with non-amplified HER2. The concordance rate in the randomly selected cases between IHC and FISH was 100%.
Conclusions: By expanding the 2+ category (11.5% of cases were re-classified as 2+) to include cases that have intense complete staining <90% instead of <30% of cells and 1+ cases that have >10% weak or non-uniform incomplete staining, the concordance rate between IHC and FISH could reach 100%.