Concordance between ER, PR, Ki67, and HER2-low expression in breast cancer by MammaTyper RT-qPCR and...

Area of Science:

• Oncology
• Molecular Diagnostics
• Biomarker Analysis

Background:

• Limited data exists on multigene tests' correlation with immunohistochemistry (IHC) on core biopsies.
• MammaTyper is a CE-marked RT-qPCR test for mRNA expression of ESR1, PGR, ERBB2, and MKI67.

Purpose of the Study:

• To evaluate the concordance of MammaTyper (RT-qPCR) with IHC for key breast cancer biomarkers.
• To assess the reliability of MammaTyper on core needle biopsies.

Main Methods:

• 133 breast cancer core needle biopsies were analyzed.
• MammaTyper results were compared to IHC for ER, PR, HER2, and Ki67.
• HER2 positivity defined by IHC 3+ or 2+ with FISH amplification; Ki67 analyzed globally and by hotspot using digital image analysis.

Main Results:

• High concordance between RT-qPCR and IHC for ESR1 (OPA 94.7%) and PR (PPA 91.5%).
• Strong agreement for ERBB2/HER2 (OPA 95%), identifying ERBB2-low cases.
• Optimal MKI67 concordance achieved with hotspot digital image analysis (OPA 87.2%).

Conclusions:

• RT-qPCR assessment of ESR1, PGR, ERBB2, and MKI67 mRNA expression shows high concordance with IHC.
• MammaTyper on core biopsies is a reliable, efficient, and reproducible alternative for breast cancer classification.
• The test aids in refining HER2-low categorisation.