P1-07-05: HER2 Status Resolution in FISH and IHC “Double Equivocal” Breast Carcinomas by Quantitative Real-Time PCR.

Abstract

Abstract Background: Clinical testing for HER2 amplification/over-expression is performed by immunohistochemistry (IHC) and/or fluorescence in situ hybridization (FISH) as outlined by the ASCO/CAP guidelines. Although these guidelines standardize testing and reporting, in a subset of patients, HER2 is equivocal by both IHC and FISH (“Double Equivocal”). These double equivocal patients represent a clinically problematic sub-group that currently lack standardized management guidelines. In this study, we utilize Quantitative Real-Time PCR (Q-RT-PCR) to resolve HER2 status in invasive breast cancer cases that could not be resolved via IHC and FISH testing. Material and Methods: FISH for HER2 was performed on 2259 invasive breast carcinomas from 1/2008 to 12/2010. In accordance with ASCO/CAP, all equivocal HER2 FISH cases were reflex tested by IHC. In double equivocal cases, RNA extraction was performed following macro-dissection using High Pure RNA Paraffin Kit (Roche Applied Biosciences, Indianapolis, IN). Q-RT-PCR was carried out using TaqMan® RNA-to-CT™ 1-Step Kit with primers and probes for HER2, B2M, and GAPDH (Applied Biosystems, Foster City, CA). Q-RT-PCR results were expressed as the relative quantification of HER2 vs. two control genes, all normalized against calibrator RNA from the MCF7 cell line. Cut off for Q-RT-PCR HER2 overexpression was set using ROC curve analysis (MedCalc, Belgium). Results: In our cohort of 2259 patients, 124 (5.5%) had an equivocal HER2 result by primary FISH testing. Reflex HER2 testing by IHC was unable to resolve the HER2 status in 35 (1.5%) patients. Detection of HER2 overexpression by Q-RT-PCR was validated using 50 FISH confirmed amplified and 50 non-amplified cases. Q-RT-PCR performed on these 2 control populations generated two non-overlapping populations and ROC curve analysis using a cut off value of 7.0 showed 100% sensitivity and specificity in detection of HER2 overexpression. Application of Q-RT-PCR in the double equivocal sub-group resulted in resolution of HER2 status in all cases, 8 HER2 positive (test value ranging from 7.12 - 15.37) and 14 HER2 negative (test value ranging from 1.05 - 6.92). Conclusion: Application of Q-RT-PCR for HER2 represents a viable approach to resolve HER2 status in cases that fail classification by both FISH and IHC. Q-RT-PCR combines the precision and high sensitivity of real-time PCR with the morphological specificity of histological evaluation and ultimately allows definitive HER2 classification at the time of initial diagnosis. This knowledge of HER2 status at the time of diagnosis allows for comprehensive neoadjuvant treatment although, additional studies correlating response to anti-HER2 therapy and HER2 status by Q-RT-PCR are warranted. Citation Information: Cancer Res 2011;71(24 Suppl):Abstract nr P1-07-05.