Unraveling the clinicopathological and molecular changes induced by neoadjuvant chemotherapy and endocrine therapy in hormone receptor-positive/HER2-low and HER2-0 breast cancer.

BACKGROUND: The characterization and comparison of gene expression and intrinsic subtype (IS) changes induced by neoadjuvant chemotherapy (NACT) and endocrine therapy in hormone receptor-positive (HR+)/human epidermal growth factor receptor 2 (HER2)-low versus HR+/HER2-0 breast cancer (BC) has not been conducted so far. Most evidence on the association of HER2 status with pathologic responses and prognosis in HR+/HER2-negative BC is controversial and restricted to NACT-treated disease. Similarly, a temporal heterogeneity in HER2 status has been described only with NACT. METHODS: We retrospectively recruited a consecutive cohort of 186 patients with stage I-IIIB HR+/HER2-negative BC treated with neoadjuvant therapy (NAT). Available diagnostic biopsies and surgical samples were characterized for main pathological features, PAM50 IS and ROR-P score, and gene expression. Associations with pathologic complete response, residual cancer burden-0/I, event-free survival (EFS) and overall survival (OS) based on HER2 status were assessed. Pre/post pathologic/molecular changes were analyzed in matched samples. RESULTS: The HER2-low (62.9%) and HER2-0 (37.1%) cohorts did not differ significantly in main baseline features, treatments administered, breast-conserving surgery, pathologic complete response and residual cancer burden-0/I rates, EFS, and OS. NAT induced, regardless of HER2 status, a significant reduction of estrogen receptor/progesterone receptor and Ki67 levels, a down-regulation of PAM50 proliferation- and luminal-related genes/signatures, an up-regulation of selected immune genes, and a shift towards less aggressive IS and lower ROR-P. Moreover, 25% of HER2-0 changed to HER2-low and 34% HER2-low became HER2-0. HER2 shifts were significant after NACT (P < 0.001), not neoadjuvant endocrine therapy (P = 0.063), with consistent ERBB2 mRNA level dynamics. HER2 changes were not associated with EFS/OS. CONCLUSIONS: HER2-low and HER2-0 status change after NAT in ∼30% of cases, mostly after NACT. Targeted adjuvant strategies should be investigated accordingly. Molecular downstaging with current chemo/endocrine agents and immunotherapy should not rely on HER2 immunohistochemical levels in HR+/HER2-negative BC. Instead, HER2-low-targeted approaches should be explored to pursue more effective and/or less toxic dimensional downstaging.

Analytical validation of HER2DX genomic test for early-stage HER2-positive breast cancer.

BACKGROUND: HER2DX, a multianalyte genomic test, has been clinically validated to predict breast cancer recurrence risk (relapse risk score), the probability of achieving pathological complete response post-neoadjuvant therapy (pCR likelihood score), and individual ERBB2 messenger RNA (mRNA) expression levels in patients with early-stage human epidermal growth factor receptor 2 (HER2)-positive breast cancer. This study delves into the comprehensive analysis of HER2DX's analytical performance. MATERIALS AND METHODS: Precision and reproducibility of HER2DX risk, pCR, and ERBB2 mRNA scores were assessed within and between laboratories using formalin-fixed paraffin-embedded (FFPE) tumor tissues and purified RNA. Robustness was appraised by analyzing the impact of tumor cell content and protocol variations including different instruments, reagent lots, and different RNA extraction kits. Variability was evaluated across intratumor biopsies and genomic platforms [RNA sequencing (RNAseq) versus nCounter], and according to protocol variations. RESULTS: Precision analysis of 10 FFPE tumor samples yielded a maximal standard error of 0.94 across HER2DX scores (1-99 scale). High reproducibility of HER2DX scores across 29 FFPE tumors and 20 RNAs between laboratories was evident (correlation coefficients >0.98). The probability of identifying score differences >5 units was ≤5.2%. No significant variability emerged based on platform instruments, reagent lots, RNA extraction kits, or TagSet thaw/freeze cycles. Moreover, HER2DX displayed robustness at low tumor cell content (10%). Intratumor variability across 212 biopsies (106 tumors) was <4.0%. Concordance between HER2DX scores from 30 RNAs on RNAseq and nCounter platforms exceeded 90.0% (Cohen's κ coefficients >0.80). CONCLUSIONS: The HER2DX assay is highly reproducible and robust for the quantification of recurrence risk, pCR likelihood, and ERBB2 mRNA expression in early-stage HER2-positive breast cancer.