Abstract
We previously reported the usefulness of droplet digital polymerase chain reaction (ddPCR) for the assessment of Human epithelial growth factor receptor 2 (HER2) gene amplification in breast cancer using formalin-fixed and paraffin-embedded sections. In our previous study, we combined HER2/CEP17 ratio (HER2 gene signals to chromosome 17 signals) with ddPCR and tumor content ratio (TCR) of each sample and determined the HER2 status by adopting a two-dimensional chart. This "ddPCR-TCR method" showed a high concordance with conventional HER2 status. In this study, we updated our method to assess the HER2 status of breast cancer in a more quantitative manner. We combined obtained data of the ddPCR ratio [Rx ] and TCR [x]; we calculated "(Rx - 1)/x + 1" for 41 samples with primary breast cancer and named the value led by this formula as "eHER2 (estimated HER2/CEP17 ratio of a tumor cell)". eHER2 was equivalent to conventional in situ hybridization (ISH) HER2/CEP17 ratio in most cases. eHER2 and ISH ratio showed a strong correlation (Spearman rank correlation ρ = 0.70, p < 0.0001). The obtained results indicated that eHER2 is a potential tool for HER2 status diagnosis in breast cancer.
Highlights
Human epithelial growth factor receptor 2 (HER2) is a member of the epidermal growth factor receptor family [1]
Correlation between HER2 IHC score and eHER2, in situ hybridization (ISH) ration and eHER2, and HER2 status according to ASCO 2013 [5] and eHER2 are shown in Fig. 2a, b and c
We reaffirmed the potential of the usefulness of droplet digital polymerase chain reaction (ddPCR) for the assessment of HER2 gene amplification in breast cancer
Summary
Human epithelial growth factor receptor 2 (HER2) is a member of the epidermal growth factor receptor family [1]. HER2 gene amplification is the main mechanism of HER2 protein overexpression [2], and HER2 gene-amplified and/or HER2 protein-overexpressed cancer is determined as HER2-positive. HER2 is positive in 10%-25% of human breast cancers, and its positivity is associated with aggressive metastatic disease and a poor prognosis. Since trastuzumab, an anti-HER2 antibody, became available in daily clinical practice, the prognosis of HER2-positive breast cancer has improved dramatically [1, 2]. HER2 protein expression is generally assessed by immunohistochemistry (IHC). It is often challenging to make consistent classification of HER2 status with IHC. HER2 gene copy number is detected using an in situ hybridization (ISH). ISH provides better diagnostic accuracy and added confidence, but it is more time-consuming, labor-intensive, and expensive compared to IHC
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