Clinical effectiveness of droplet digital polymerase chain reaction technology for human epidermal growth factor receptor 2/neu gene testing in breast cancer compared to conventional methods

Objectives: Breast cancer (BC) is the most common cancer in women worldwide and has poor survival outcomes. The human epidermal growth factor receptor 2 (HER2), a key promoter of tumor progression and metastasis, is overexpressed or amplified in 15–20% of BC cases, leading to worse prognosis. The introduction of anti-HER2 monoclonal antibodies has significantly improved survival in advanced HER2-positive BC. Current HER2 testing in routine diagnostic practice relies on immunohistochemistry (IHC) and in situ hybridizations (ISH) techniques as US Food and Drug Administration-approved methods. However, these standard methods still have some limitations related to subjectivity, reproducibility, accuracy, and cost. To overcome these challenges, this study investigated droplet-based digital polymerase chain reaction (ddPCR) as a breakthrough technology for absolute DNA quantification. Methods: The ddPCR is a reliable third-generation PCR-based technology that has higher sensitivity, accuracy, and reproducibility. The HER2 gene status testing was assessed using ddPCR in a retrospective cohort of 36 formalin-fixed and paraffin-embedded tissues from BC patients with invasive ductal carcinoma. Results: Our results showed that ddPCR has very high concordance rates of 81% and 83% with IHC and brightfield double ISH (BDISH), respectively. Conclusion: These findings highlight the high accuracy and concordance of ddPCR with both BDISH and IHC, emphasizing its potential usefulness for HER2 testing in BC. After further optimization and standardization in larger cohorts, ddPCR hold the promise to become a rapid, reliable, and cost-effective alternative method suitable for the accurate assessment of HER2 gene status and other amplification-based genes for oncotherapies.