Highly Sensitive Droplet Digital PCR Method for Detection of EGFR-Activating Mutations in Plasma Cell-Free DNA from Patients with Advanced Non-Small Cell Lung Cancer

Epidermal growth factor receptor (EGFR) mutation testing in plasma cell-free DNA from Lung cancer patients is an emerging clinical tool. However, compared with tissue testing, the sensitivity of plasma testing is not yet satisfactory because of the highly fragmented nature of plasma cell-free DNA, Low fraction of tumor DNA, and Limitations of available detection technologies. We therefore developed a highly sensitive and specific droplet digital PCR method for plasma EGFR mutation (exon19 deletions and L858R) testing. Plasma from 86 EGFR-tyrosine kinase inhibitor-naive lung cancer patients was tested and compared with EGFR mutation status of matched tumor tissues tested by amplification refractory mutation system. By using EGFR mutation-positive cell DNA, we optimized the droplet digital PCR assays to reach 0.04% sensitivity. The plasma testing sensitivity and specificity, compared with the matched tumor tissues tested by amplification refractory mutation system, were 81.82% (95% CI, 59.72%-94.81%) and 98.44% (95% CI, 91.60%-99.96%), respectively, for exon19 deletions, with 94.19% concordance rate (kappa = 0.840; 95% CI, 0.704-0.976; P < 0.0001), whereas they were 80.00% (95% CI, 51.9%-95.67%) and 95.77% (95% CI, 88.14%-99.12%), respectively, for L858R, with 93.02% concordance rate (kappa = 0.758; 95% CI, 0.571-0.945; P < 0.0001). The reported highly sensitive and specific droplet digital PCR assays for EGFR mutation detection have potential in clinical blood testing.