Assessment of ESR1, PGR, ERBB2, and MKI67 mRNA in Hormone Receptor-Positive Early Breast Cancer: A Cross-Sectional Study

Abstract

Background and aims: Hormone receptors are expressed in 70% of breast cancers and are the major biomarkers for tailoring treatment in early-stage breast cancer. In clinical routine, immunohistochemistry (IHC) is used to assess estrogen receptor (ER), progesterone receptor (PR), HER2, and Ki67 protein expression. However, IHC procedure is challenged with pre-analytical and analytical variability. Pathologist interpretation of IHC results can vary, and discordant results between local and reference laboratories have been reported. Using mRNA-based tests may be a more robust, reliable, and standardized method to assess these important breast cancer biomarkers. This study aimed to assess the concordance between real-time PCR and IHC results.

Methods: In this study, we analyzed 178 early-stage hormone receptor-positive breast tumors. IHC for ER, PR, HER2, and Ki67 had been previously performed for the study samples at local laboratories. For samples with HER2 IHC score 2+, Fluorescence In Situ Hybridization was performed. ESR1 (encoding ER), PGR (encoding PR), ERBB2 (encoding HER2), and MKI67 (encoding Ki67) mRNA expression were determined using TaqMan gene expression assays.

Results: The overall concordance between mRNA expression results and their corresponding IHC markers was 95.9% for ESR1/ER, 79.3% for PGR/PR, and 100% for ERBB2/HER2. There was a moderate correlation between MKi67 mRNA values and Ki67 IHC. ESR1 expression was significantly lower in tumors of younger patients (p < 0.001). No statistically significant correlation between age at cancer diagnosis and ER IHC was identified. Higher ESR1 and MKI67 mRNA expression was associated with worse pathological characteristics.

Conclusions: PCR-based classification of breast tumors in a central laboratory may be used to confirm the available IHC results performed at local laboratories and add valuable information for patient management. mRNA-based biomarkers may be promising for more standardized breast cancer management.

Keywords: HER2 receptor; breast cancer; estrogen receptor; ki67; progesterone receptor.

Figure 1

Scatter plots of the distribution of mRNA expression and IHC. (A) ESR1 mRNA/ER IHC; (B) PGR mRNA/PR IHC; (C) MKI67 mRNA/Ki67 IHC; (D) Boxplot of distribution of ERBB2 mRNA expression and HER2 IHC. Each dot represents a patient. Abbreviations: Ct, cycle threshold; ER, estrogen receptor; HER2, human epidermal growth factor receptor 2; IHC, immunohistochemistry; PR, progesterone receptor; r, Spearman's rank correlation.

Figure 2

Expression of estrogen receptor mRNA (ESR1) and ER protein in older (> 60 years) and younger (≤ 60 years) patients. (A) ESR1 mRNA; (B) ER IHC. Two‐side Wilcoxon rank‐sum test was used to estimate the p values. Each dot represents a patient, the horizontal red line represents the median ESR1/ER expression in each patient age group. Abbreviations: Ct, cycle threshold; ER, estrogen receptor; IHC, immunohistochemistry.

Figure 3

A scatter plot depicting the distribution of tumor ESR1 and MKI67 mRNA content. Abbreviations: Ct, cycle threshold; r, Spearman's rank correlation.

Figure 4

Boxplot of association between ER expression and tumor pathologic characteristics. Two‐side Wilcoxon rank‐sum test was used to estimate the p values. (A) ESR1 mRNA quantity/tumor size > 2 cm or ≤ 2 cm; (B) ER IHC percentage/tumor size > 2 cm or ≤ 2 cm; (C) ESR1 mRNA quantity/lymph node involvement; (D) ER IHC percentage/lymph node involvement; (E) ESR1 mRNA quantity/lympho‐vascular invasion; (F) ER IHC percentage/lympho‐vascular invasion.