A Retrospective Population-Based Comparison of HER2 Immunohistochemistry and Fluorescence In Situ Hybridization in Breast Carcinomas: Impact of 2007 American Society of Clinical Oncology/ College of American Pathologists Criteria

Abstract

Context.—In 2007 the American Society of Clinical Oncology/College of American Pathologists made new recommendations for HER2 testing and redefined HER2 positivity. Objective.—To analyze results from simultaneous HER2 testing with immunohistochemistry and fluorescence in situ hybridization (FISH) in 2590 invasive breast carcinomas between 2002 and 2010, using 2 scoring systems. Design.—Cases from between 2002 and 2006 were scored by using original US Food and Drug Administration criteria (N = 1138) and those from between 2007 and 2010 were evaluated according to American Society of Clinical Oncology/College of American Pathologists criteria (N = 1452). Concordance between testing methods and clinicopathologic associations were determined. Results.—Overall concordance between immunohistochemistry/FISH in the 9-year period was 96.2% (κ = 0.82), and positive concordance was lower. After 2007, the proportion of HER2/neu-positive and HER2/neu-negative cases was not significantly changed when using immunohistochemistry (10.5% versus 8.9%, P = .22 and 69.4% versus 63%, P = .13, respectively), but the number of equivocal cases was higher (19.9% versus 28%, P < .001). While the proportion of negative cases by FISH remained unchanged after 2007 (86.5% versus 88.2%, P = .76), the number of positive cases was lower (13.4% versus 9.2%, P < .001). In addition, 38 cases (2.6%) were FISH equivocal, 16 of which were also equivocal by immunohistochemistry. Overall, immunohistochemistry/FISH concordance was 95.9% between 2002 and 2006 (κ = 0.82) and 96.4% after 2007 (κ = 0.82). However, an approximately 13% lower positive assay concordance was noted in the last period. Conclusions.—Application of American Society of Clinical Oncology/College of American Pathologists recommendations is associated with comparable overall immunohistochemistry/FISH concordance, reduced positive concordance, and increased equivocal results.

Implications of the Updated 2013 American Society of Clinical Oncology/College of American Pathologists Guideline Recommendations on Human Epidermal Growth Factor Receptor 2 Gene Testing Using Immunohistochemistry and Fluorescence In Situ Hybridization for Breast Cancer

“…Although the stricter criteria of 30% The close association between HER2/neu gene amplification and protein overexpression in breast carcinomas was evident by the higher FISH ratios as well as HER2/neu copy numbers with higher HER2/neu membranous immunoreactivity as confirmed by other studies (Tables 5 and 6). 18 In addition, most IHC2þ cases were negative for HER2/neu FISH amplification (81.6% (418 of 512; Table 1), which was a finding similar to that of others. 16,18 However, the number of equivocal IHC/negative FISH cases decreased with the revised 2013 ASCO/CAP guidelines because of an increase in the number of negative FISH cases with an average HER2/neu copy number of at least 4.0 but less than 6.0 that were reclassified to equivocal.…”

“…18 In addition, most IHC2þ cases were negative for HER2/neu FISH amplification (81.6% (418 of 512; Table 1), which was a finding similar to that of others. 16,18 However, the number of equivocal IHC/negative FISH cases decreased with the revised 2013 ASCO/CAP guidelines because of an increase in the number of negative FISH cases with an average HER2/neu copy number of at least 4.0 but less than 6.0 that were reclassified to equivocal. In fact, the number of equivocal FISH cases increased from 0.7% (4 of 590) to 9.5% (56 of 590) (Table 4) as confirmed by Pu et al 33 In addition, equivocal IHC/equivocal FISH cases also increased from 0.7% (4 of 590) to 8.3% (49 of 590) ( Tables 1 and 2).…”

“…18 Slamon et al 19 reported that breast cancer cases with gene amplification and overexpression may lose membrane staining after paraffin embedding. Poor standardization of fixative methods can lead to loss of antigenicity, resulting in false-negative IHC results.…”

Assessment of HER2 testing patterns, HER2+ disease, and the utilization of HER2-directed therapy in early breast cancer

“…Our study results indicate that this guideline change may have resulted in reclassifying approximately 5.9% of IHC3+ tumors to IHC2+, which is consistent with other reports of increased IHC2+ tumors during this time period 22,23. Additionally, although not significant, the proportion of HER2+ patients did decrease after guideline publication (4.2%), which is consistent with other reports documenting a 3% difference 23.…”

Comparison of immunohistochemistry within situhybridization methods: discrepancy resolution and implications for low-mid income countries

“…5 It was identified from a retrospective review of 2590 cases that IHC and FISH had a concordance rate of 96%, which is better with negative IHC. 23 Two basic points in the recommendations are worth noting; firstly, diagnosis HercepTest score >2+, and makes it perhaps illogical to perform an ISH test on a specimen if the IHC is negative. It is pertinent to emphasize that this appraised study reported a discrepancy of 18% (31/174), which translates to a concordance of 82%.…”