Quantitative assessment of HER2 gene amplification of breast cancer using droplet digital PCR.

Kazutaka Otsuji, Takeshi Sasaki, Masahiko Tanabe, Yasuyuki Seto

Pathology international 2021 Aug

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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. © 2021 Japanese Society of Pathology and John Wiley & Sons Australia, Ltd.

Citation

Kazutaka Otsuji, Takeshi Sasaki, Masahiko Tanabe, Yasuyuki Seto. Quantitative assessment of HER2 gene amplification of breast cancer using droplet digital PCR. Pathology international. 2021 Aug;71(8):538-547