Comparison of HercepTest™ mAb pharmDx (Dako Omnis, GE001) with Ventana PATHWAY anti-HER-2/neu (4B5) in breast cancer: correlation with HER2 amplification and HER2 low status

Abstract

Performance of the new CE-IVD-marked HercepTest™ mAb pharmDx (Dako Omnis) assay (HercepTest (mAb)) was compared against the PATHWAY® anti-HER-2/neu (4B5) (PATHWAY 4B5) assay using 119 pre-selected breast cancer samples covering the entire range of HER2 immunohistochemistry (IHC) expression scores (0, 1 + , 2 + , 3 +). The sensitivity and specificity of both assays were assessed based on consensus IHC scores and amplification status, as determined by fluorescence in situ hybridization (FISH) according to 2018 ASCO/CAP testing guidelines. There was a high concordance between results from the HercepTest (mAb) and PATHWAY 4B5 assays for HER2-negative (IHC 0, 1 + , 2 + and FISH negative) and HER2-positive (IHC 3 + , 2 + and FISH positive) breast carcinomas (98.2%). Regarding individual IHC scores, complete agreement was achieved in 69.7% (83/119) of cases, and all but one of the discordant cases were due to higher HER2-status scoring using the HercepTest (mAb). Thus, more tumors were overscored as IHC 2 + by HercepTest (mAb) (27 versus 15) as evidenced by their lower FISH positivity rate (48.1% versus 80%). However, two amplified tumors identified as IHC 2 + by HercepTest (mAb) were missed by PATHWAY 4B5 (IHC 1 +). Four additional cases identified as IHC 2 + by HercepTest (mAb), with FISH ratio < 2 but elevated gene counts (≥ 4 to < 6), were recorded negative by PATHWAY 4B5. The HercepTest (mAb) detects HER2 expression with higher sensitivity in tumors with gene amplification (ISH group 1) and increased gene counts (ISH group 4) as well as in HER2-low tumors (HER2 IHC2 + /FISH negative or IHC 1 +). Future studies will demonstrate whether this translates into improved patient selection especially for new HER2-directed therapies.

Keywords: Dako Omnis; FISH; HER2; HercepTest (mAb); IHC; Invasive breast carcinoma; PATHWAY 4B.

Fig. 1

Schematic illustration of the study design

Fig. 2

Comparison of HER2 detection by both IHC assays (HercepTest (mAb) versus PATHWAY 4B5). A, B Non-specific cytoplasmic granular staining by using PATHWAY 4B5 not visible by using HercepTest (mAb). C, D Weak to moderate staining within some accompanying normal duct epithelium by using HercepTest (mAb), barely visible by using PATHWAY 4B5. E, F Comparison of discordantly scored (HercepTest (mAb) IHC 2 + , PATHWAY 4B5 IHC 1 +) in a FISH HER2-positive sample (#86). Scale bar: 200 µm (magnification 10 ×). Inserts show enlargements of the respective photomicrographs (magnification 20 ×)

Fig. 3

Comparison of HercepTest (mAb) (HcT) and PATHWAY 4B5 (4B5) with respect to IHC scores and FISH status. A According to ASCO/CAP IHC scoring, all ISH positive cases (filled symbols) were scored IHC 3 + or IHC 2 + by using HcT. In two of the ISH positive tumors, 4B5 was IHC 1 + (red circle). B Detailed analysis of 53 tumors scored as IHC 0 according to ASCO/CAP by 4B5 (see cases within blue frames in A) with 41 tumors showing no staining and 12 cases with HER2 expression in < 10% of cells (grey area). Using HcT, 16 cases were shifted up to IHC score 1 + and in 3 cases to IHC 2 + (matching to HER2-low category). Fourteen cases were shifted from no staining by 4B5 to some staining (< 10%, grey zone) by HcT (matching to HER2 ultra-low category: 0 < 1 +). IHC scores were unchanged in 20 cases (19 IHC 0, 1 IHC 0 < 1 +)