Targetable ERBB2 mutation status is an independent marker of adverse prognosis in estrogen receptor positive, ERBB2 non-amplified primary lobular breast carcinoma: a retrospective in silico analysis of public datasets

Abstract

Background: Invasive lobular carcinoma (ILC) accounts for 10-15% of primary breast cancers and is typically estrogen receptor alpha positive (ER+) and ERBB2 non-amplified. Somatic mutations in ERBB2/3 are emerging as a tractable mechanism underlying enhanced human epidermal growth factor 2 (HER2) activity. We tested the hypothesis that therapeutically targetable ERBB2/3 mutations in primary ILC of the breast associate with poor survival outcome in large public datasets.

Methods: We performed in silico comparison of ERBB2 non-amplified cases of ER+ stage I-III primary ILC (N = 279) and invasive ductal carcinoma (IDC, N = 1301) using METABRIC, TCGA, and MSK-IMPACT information. Activating mutations amenable to HER2-directed therapy with neratinib were identified using existing functional data from in vitro cell line and xenograft experiments. Multivariate analysis of 10-year overall survival (OS) with tumor size, grade, and lymph node status was performed using a Cox regression model. Differential gene expression analyses by ERBB2 mutation and amplification status was performed using weighted average differences and an in silico model of response to neratinib derived from breast cancer cell lines.

Results: ILC tumors comprised 17.7% of all cases in the dataset but accounted for 47.1% of ERBB2-mutated cases. Mutations in ERBB2 were enriched in ILC vs. IDC cases (5.7%, N = 16 vs. 1.4%, N = 18, p < 0.0001) and clustered in the tyrosine kinase domain of HER2. ERBB3 mutations were not enriched in ILC (1.1%, N = 3 vs. 1.8%, N = 23; p = 0.604). Median OS for patients with ERBB2-mutant ILC tumors was 66 months vs. 211 months for ERBB2 wild-type (p = 0.0001), and 159 vs. 166 months (p = 0.733) for IDC tumors. Targetable ERBB2 mutational status was an independent prognostic marker of 10-year OS-but only in ILC (hazard ratio, HR = 3.7, 95% CI 1.2-11.0; p = 0.021). Findings were validated using a novel ERBB2 mutation gene enrichment score (HR for 10-year OS in ILC = 2.3, 95% CI 1.04-5.05; p = 0.040).

Conclusions: Targetable ERBB2 mutations are enriched in primary ILC and their detection represents an actionable strategy with the potential to improve patient outcomes. Biomarker-led clinical trials of adjuvant HER-targeted therapy are warranted for patients with ERBB2-mutated primary ILC.

Keywords: Adjuvant; Breast cancer; ERBB2; HER2; Lobular; Mutation; Prognosis; Therapeutic biomarker.

Fig. 1

Rate of ERBB2 and ERBB3 mutations and their spatial distribution on HER2/3 in ILC and IDC. ERBB2mut were found to be a enriched in ILC (yellow bar) vs. IDC (blue bar) and b clustered in the tyrosine kinase domain of HER2; c ERBB3mut occurred at lower frequency, with the high-frequency outlier in IDC coding for known oncogenic HER3 kinase domain alteration E928G (N = 6). Y-axes show the number of cases harboring at least one ERBB2/3 mutation at a specific amino acid (aa) of HER2/3, shown along the x-axes. Yellow-filled circles indicate oncERBB2mut. Extracellular domains of HER2/3: Receptor L, Furin-like and Growth Factor Receptor IV; intracellular: tyrosine protein kinase. *p < 0.001; n/s = not significant

Fig. 2

OS by ERBB2 mutational status in ILC (left) and IDC (right). Gray line indicates ERBB2 wild-type cases; blue line indicates cases with at least one ERBB2mut

Fig. 3

Univariate and multivariate analyses of 10-year OS in N = 279 cases of ER+, ERBB2 non-amplified ILC. Gray square dot indicates hazard ratio (HR) in univariate analysis and the gray bar indicates the 95% confidence interval (CI). Significant prognostic variables in univariate analyses (where 95% CI does not span HR = 1) are included in multivariate analysis, shown in blue. For each variable, cases with unknown values are excluded from the analysis

Fig. 4

A novel gene signature of HER2 activity incorporating ERBB2mut, ERBB2 amplification, and clinical HER2 status. a Generation of a 20-gene signature of HER2 activity. The upper Venn diagrams show the overlap between the top 500 DEGs by WAD score for METABRIC amplified vs. non-amplified, ERBB2 mutant vs. wild-type, and TCGA HER2+ vs. HER2−. Upregulated DEGs are shaded blue and down-regulated DEGs yellow. ERBB2mut and oncERBB2mut vs. wild-type are analyzed separately, and the overlap combined in the lower Venn diagrams. b Comparison with an established 24-gene signature of HER pathway activation [31], using a gene signature (genesig) score derived from multivariate analysis of response to neratinib in breast cancer cell lines. Cases with ERBB2mut (gray lines) and oncERBB2mut (blue lines) clustered in the upper quartile of normalized genesig scores for the novel signature but not the established signature. c 10-year OS analysis of cases in the current study stratified by histological subtype and novel genesig score (upper vs. lower quartiles) indicates that ERBB2mut-associated DEGs are prognostic in ILC but not IDC. GE, geneset enrichment