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Updated: Jul 7, 2025

Optimization of a Multiplex RNA-based Expression Assay Using Breast Cancer Archival Material
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Optimization of a Multiplex RNA-based Expression Assay Using Breast Cancer Archival Material

Published on: August 1, 2018

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Correlation of HER2 Protein Level With mRNA Level Quantified by RNAscope in Breast Cancer

Xiaoxian Li1, Ji-Hoon Lee2, Yuan Gao1

  • 1Department of Pathology and Laboratory Medicine, Emory University, Atlanta, Georgia.

Modern Pathology : an Official Journal of the United States and Canadian Academy of Pathology, Inc
|December 22, 2023
PubMed

Insights

RNAscope accurately measures HER2 expression in breast cancer, outperforming current immunohistochemical (IHC) assays for HER2-low cases. This method shows promise in identifying patients likely to respond to trastuzumab deruxtecan (T-DXd) therapy.

Area of Science:

  • Oncology
  • Molecular Diagnostics
  • Biomarker Research

Background:

  • Trastuzumab deruxtecan (T-DXd) is approved for HER2-positive and HER2-low metastatic breast cancer.
  • Current HER2 immunohistochemical (IHC) assays struggle to accurately assess HER2-low breast cancers for T-DXd eligibility.
  • Improved methods are needed to identify patients who will benefit from T-DXd therapy.

Purpose of the Study:

  • To evaluate RNAscope as a novel assay for quantifying HER2 expression in breast cancer.
  • To compare RNAscope results with existing HER2 IHC assays (PATHWAY and HercepTest).
  • To correlate HER2 expression levels measured by RNAscope with patient response to T-DXd treatment.

Main Methods:

  • HER2 expression was assessed in 526 breast cancer tissue microarray cores using PATHWAY and HercepTest IHC assays.
  • RNAscope was used to measure HER2 RNA levels in the same cores.
  • HER2 protein levels were quantified using immunofluorescence and mass spectrometry in a subset of cores.
  • RNAscope was performed on metastatic biopsies from 23 patients treated with T-DXd, correlating results with response rates.

Main Results:

  • HER2 RNA levels by RNAscope strongly correlated with HER2 protein levels and IHC H-scores (P < .0001).
  • No significant difference in protein or RNA levels was observed for IHC scores of 0, ultralow, and 1+.
  • Significantly higher RNA levels were found in T-DXd responders (6.4 dots/cell) compared to non-responders (2.6 dots/cell) (P = .030).

Conclusions:

  • RNAscope is a reliable and objective assay for quantifying HER2 expression in breast cancer.
  • RNAscope demonstrates potential as an alternative to current IHC assays, particularly for HER2-low breast cancer.
  • This assay may improve patient selection for trastuzumab deruxtecan (T-DXd) therapy.
Keywords:
HER2RNAscopeT-DXdbiomarkerpredictivequantification

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