Quantitative HER2 protein levels predict outcome in fluorescence in situ hybridization‐positive patients with metastatic breast cancer treated with trastuzumab

Abstract

BACKGROUND: Only a portion of breast cancer patients currently selected for trastuzumab therapy respond. METHODS: Using a novel assay (HERmark) to quantify total human epidermal growth factor receptor 2 (HER2) expression, the authors examined outcomes in 102 trastuzumab-treated metastatic breast cancer patients previously assessed as immunohistochemistry (IHC) 3þ by local but not central IHC, or fluorescence in situ hybridization (FISH) positive, and then retested by central FISH. RESULTS: Of 102 MBC patients previously scored as IHC 3þ or 2þ/FISHpositive and treated with trastuzumab-containing regimens, 98 had both central FISH and HER2 total expression values. Sixty-six of 76 central FISH-positive patients (87%) had high HER2 total expression levels (concordant positive), and 19 of 22 central FISH-negative patients (86%) were HER2 total expression low (concordant negative). Fourteen percent (3 of 22) of central FISH-negative patients were HER2 total expression high (discordant HER2 total expression high), and 13% (10 of 76) of central FISH-positive patients were HER2 total expression low (discordant HER2 total expression low). The concordant positive group had a significantly longer time to progression (TTP, median ¼ 11.3 months) compared with the concordant negative group (median TTP, 4.5 months; hazard ratio [HR] ¼ 0.42, P < .001), and also compared with the discordant HER2 total expression low group (median TTP, 3.7 months; HR ¼ 0.43, P ¼ .01). The discordant HER2 total expression low group behaved similarly compared with concordant negatives (HR ¼ 1, P ¼ .99). In analyses restricted to central FISH-positive patients only (n ¼ 77), Cox proportional hazards multivariate regression identified HER2 total expression as an independent predictor of TTP (HR ¼ 0.29, P ¼ .0015) and overall survival (HR ¼ 0.19, P < .001). CONCLUSIONS: A subset of patients with HER2 gene amplification by FISH express low levels of HER2 protein and have reduced response to trastuzumab-containing therapy, similar to FISH-negative

Quantitation of p95HER2 in Paraffin Sections by Using a p95-Specific Antibody and Correlation with Outcome in a Cohort of Trastuzumab-Treated Breast Cancer Patients

“…Correlation of p95 expression with clinical outcomes High HER2 expression, as measured by the VeraTag HER2 assay, and high FISH copy number (HER2 FISH/ CEP17 > 2.2) were previously shown to be significantly correlated with longer progression-free survival (PFS) following trastuzumab treatment in this cohort (23). Here, we sought to test the hypothesis that p95 measurements could be used to define subgroups of patients with different outcomes within the HER2-overexpressed or HER2 FISH-amplified subgroups.…”

“…To test whether the current p95 assay can be used to predict different outcomes for patients receiving trastuzumab, 93 tumors from a cohort of trastuzumab-treated metastatic breast cancer patients were measured for HER2 and p95 using VeraTag assays. Clinical characteristics and HER2 measurements for the current cohort were described previously (23). The VeraTag p95 assay was done on the FFPE tumor sections in eight batches.…”

“…Seventy-two percent of p95 signals from the tumors in the trastuzumab-treated cohort were found to be above this sensitivity cutoff. When considering only the tumors with overexpressed HER2 using the VeraTag HER2 assay (21)(22)(23)(24) or those that were HER2 fluorescence in situ hybridization (FISH) amplified, 81% and 79%, respectively, of the p95 signals fell above this sensitivity limit.…”

“…The cutoff for p95 was optimized to maximize the hazard ratio (HR) between patients with tumor p95 expression above versus below the cutoff within the HER2-positive subgroup. This cutoff was used along with the previously defined HER2 cutoff (22,23) to define three groups: low HER2, high HER2 with low p95, and high HER2 with high p95. PFS and overall survival (OS) Kaplan-Meier plots for these three groups are shown in Fig.…”

Quantitative Measurements of Tumoral p95HER2 Protein Expression in Metastatic Breast Cancer Patients Treated with Trastuzumab: Independent Validation of the p95HER2 Clinical Cutoff

“…These cutoffs were derived from the <5th percentile of centrally determined HER2 positives and the >95th percentile of centrally determined HER2 negatives, respectively, within a reference database of 1,090 breast cancer patient samples. The cutoff of 13.8 RF/mm 2 that best discriminated better versus worse patient outcomes on trastuzumab-based therapy was earlier determined in an independent cohort of patients (12). This cutoff was used in all clinical analyses in the current study to define HER2 positivity by the VeraTag assay.…”