Abstract P5-02-07: Effect of the new 2013 ASCO / CAP guidelines on HER2 reporting
Authors: Gulbahce H  Evin , Factor Rachel E , Downs-Kelly Erinn , Coppin Margaret , Geiersbach Katherine B 
Published: May 2015

Introduction: In 2013 ASCO/CAP published new guidelines for HER2 testing to decrease false negatives. We retrospectively classified cases submitted to a national reference laboratory for HER2 testing using the new guidelines in order to 1) see the overall effect of the 2013 vs 2007 guidelines and 2) predict shifts in interpretation of different HER2 testing methods in the future.

M&M: Our laboratory offers HER2 immunohistochemistry (IHC) by HercepTest (Dako) or 4B5 (Ventana) and HER2 dual probe FISH (Abbott Molecular). HER2 IHC and/or FISH tests performed between 1/2010-8/2013, originally scored with the 2007 guidelines, were reclassified with the 2013 guidelines. For IHC, the guideline scores of 0, 1+, 2+ and 3+ were recorded along with intensity (weak, moderate, strong) and % circumferential staining. For FISH, the HER2 and CEP 17 copy number per cell, and HER2:CEP 17 ratio were recorded.

Results: 2358 samples submitted for HER2 FISH were available for review. Using the 2007 guidelines, 246 (10.4%) were amplified (Amp), 62 (2.7%) equivocal (Eq), and 2050 (86.9%) were non-amplified (NA). 29/62 (46.8%) FISH Eq cases had HER2:CEP17 ratio between 2.0-2.2, 1 (1.6%) had HER2 copy number &gt;6 per cell. Therefore 30/2358 (1.3%) of all FISH tests previously classified as Eq would be reclassified as Amp following new guidelines increasing the overall FISH Amp rate by 12.5% to 11.7%. Over the same time period, 4043 HER2 IHC tests were performed using old guidelines 1097/4043 (27.1%) of which were Eq (2+). 731/1097 (66.6%) had reflex FISH requested on 2+ IHC cases. 24/731 (3.3%) did not have an iterpretable FISH result. Using the 2007 guidelines, 49 (6.9%) of the 2+ cases were FISH Amp, 23 (3.3%) remained Eq, 635 (89.8%) were NA. Using the new guidelines, an additional 8 (1.1%) of these 707 reflex FISH would be classified as Amp (7 cases due to HER2:CEP17 ratio 2.0 to 2.2 and one case for HER2 copy number &gt;6). Also 8 NA cases would be reclassified as Eq due to a HER2 copy number between 4 and 5.9. With the new guidelines, the overall FISH Amp rate identified from reflex 2+ IHC is 8.1%. 507/707 (71.7%) of HER2 Eq (2+) cases reflexed to FISH had 10-30% circumferential staining (8 strong; 136 moderate; 363 weak). HER2 Amp rates for these are shown in Table 1.

HER2 Amplification Status of IHC Equivocal (2+) Cases by Percent Membrane StainingIHC 2+FISH Amplified (2013 Guidelines) (%)2+ Cases (All)57/707 (8.1%)2+ Cases, 10-30% Membrane Staining37/507 (7.3%)-------Strong-------1/8 (12.5%)-------Moderate-------16/136 (11.8%)-------Weak-------20/363 (5.5%)

Conclusion: 2013 guidelines will identify a higher % (1.1% for FISH) of eligible patients for targeted therapy. In this series, 2+ IHC cases with reflex FISH testing also had higher Amp rates by 2013 guidelines (8.1% vs 6.9%). Evaluating these rates over time will help assess the effect of the change in the scoring criteria. Amp rates for Eq (2+) IHC cases with 10-30% strong and moderate membrane staining are similar, although only the former group is classified as positive (3+) following new guidelines and would not be retested by FISH. Cases with less than 30% membrane staining may represent a biological spectrum that is not well represented by current IHC testing guidelines, and FISH confirmation on these cases may be justified.

Citation Format: H Evin Gulbahce, Rachel E Factor, Erinn Downs-Kelly, Margaret Coppin, Katherine B Geiersbach. Effect of the new 2013 ASCO / CAP guidelines on HER2 reporting [abstract]. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr P5-02-07.