RNAscope-based HER2 mRNA detection shows high concordance with fluorescence in situ hybridization in invasive breast
Wei Hua1, Yunhe Gu1, Ying Yuan1
1Department of Pathology, The First Affiliated Hospital of Harbin Medical University, Harbin, China.
Background:
Human epidermal growth factor receptor 2 (HER2) status is critical for guiding targeted therapy in invasive breast cancer (BC). Immunohistochemistry (IHC) is routinely used for HER2 screening, but equivocal (IHC 2+) cases require confirmatory testing. RNAscope is an emerging RNA in situ hybridization technique with proven consistency and sensitivity. We investigated whether RNAscope can reliably determine HER2 status and enhance diagnostic concordance with FISH in IHC 2+ invasive ductal carcinoma (IDC).
Methods:
In this retrospective study, 104 IDC cases from January 2020 to January 2024 were reviewed. Thirty-five cases with IHC 2+ scores were randomly selected. Each case underwent RNAscope and fluorescence in situ hybridization (FISH) for HER2. Concordance between RNAscope and FISH results was evaluated using Cohen's kappa statistic. Next-generation sequencing (NGS) was performed on discordant cases to confirm HER2 gene status.
Results:
RNAscope and FISH results were concordant in 85.7% (30/35) of IHC 2+ cases [κ=0.678, 95% confidence interval (CI): 0.425-0.872], indicating substantial agreement. RNAscope detected HER2 positivity in all 12 FISH-positive cases (100% agreement) and in 5 of 23 FISH-negative cases, identifying additional positive cases. Among the 5 discordant cases, NGS confirmed HER2 amplification or overexpression in 4 (80%) of the RNAscope-positive/FISH-negative cases. These findings suggest that RNAscope may detect HER2-positive cases missed by FISH.
Conclusions:
RNAscope shows high agreement with FISH in determining HER2 status in IHC 2+ IDC. RNAscope may serve as an effective adjunct to current HER2 testing, offering a sensitive alternative for ambiguous cases.
