Abstract P3-05-03: HER2-CONNECT® pathologist-assisted image analysis algorithm for HER2 IHC interpretation improves correlation with HER2 FISH results

Abstract

Abstract Background: HER2 testing by immunohistochemistry (IHC) is prone to inter-observer variability and subjective interpretation. Pathologist-assisted digital image analysis is recommended in the CAP/ASCO guidelines to improve interpretive consistency. As a quality benchmark, HER2 IHC results should correlate with HER2 fluorescence in-situ hybridization (FISH) in >95% of positive and negative cases. HER2-CONNECT® (Visiopharm, Hoersholm Denmark) is a digital analysis algorithm that scores stained membrane interconnectivity rather than relying solely on staining of individual cells. As such, it can be thought of as a surrogate for the so-called “chickenwire” pattern characteristic of true HER2 positive tumors. In this study we applied HER2-CONNECT® analysis with pathologist quantitative interpretation (HC+PQI) to a set of breast tumors with known HER2 FISH status to assess concordance. Design: Breast carcinoma tissue sections previously stained with HER2 IHC (HercepTest) and interpreted manually were retrospectively re-submitted for HC+PQI. These included core and excisional biopsies from primary and metastatic sites. Fixation times were documented within recommended guidelines. HER2 FISH (PathVysion) was performed on all cases. Using connectivity scores on a scale of 0 - 1.0 from the analyzed regions, a pathologist determined the overall% of HER2 positive tumor cells in the sample (since HER2-CONNECT reports connectivity, but not tumor cell quantitation) and reported a final score per CAP/ASCO guidelines (<10% = 1+, 10-30% = 2+, >30% = 3+). Results: 190 cases comprised the analysis set, including 77 3+, 73 2+, and 40 0/1+ as scored in the original reports. 66 cases were HER2 FISH amplified (64/77, 83% of the original 3+ cases and 2/73, 2.7% of 2+ cases) and 6 cases were FISH equivocal. None of the 0/1+ cases were HER2 FISH amplified. Using HC+PQI, the new scores were 67 3+, 68 2+, and 55 1+. Correlation between HC+PQI and HER2 FISH was 95.5% (64/67) for 3+/amplified and 100% (55/55) for <2+/nonamplified (overall concordance 97.5%). Using FISH as the gold standard, the HC+PQI interpretation reduced the false positive rate from 13% (15/108) to 3% (4/108). 17 of 63 HER2 nonamplified samples originally scored 2+ were changed to 1+ on HC+PQI (i.e. reduction of FISH testing by 27% (17/63)). Conclusions: Relative to the original report scores, HC+PQI improved correlation with HER2 FISH and reduced the overall number of 2+ results (potentially reducing the number of FISH tests required). These data also objectively highlight the importance of the “chickenwire” pattern in positive result interpretation for HER2. Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr P3-05-03.