Molecular Analysis of Circulating Cell-Free DNA from Lung Cancer Patients in Routine Laboratory Practice

Circulating cell-free DNA (cfDNA), which is isolated from blood plasma, represents a noninvasive source for the detection of mutations conferring resistance against epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors in non-small-cell lung cancer patients. In advanced disease stages, performing regular biopsies is often not possible because of the general health condition of the patients. Furthermore, a biopsy of a single tumor lesion or metastasis may not reflect the heterogeneous genotype of the tumor and its metastases. Plasma cfDNA represents an alternative material for molecular monitoring of patients under therapy. Herein, we present a cross-platform comparison of three different molecular methods [digital PCR, next-generation sequencing (NGS), and quantitative PCR] to detect clinically relevant mutations in cfDNA. We validated our workflow with commercially available cfDNA reference material (5.0%, 1.0%, and 0.1% mutation frequency, respectively). Digital PCR and NGS detect reliably 0.1% allele frequency of the EGFR p.T790M mutation. Furthermore, we analyzed 55 cfDNA preparations from patients with lung cancer to compare reliability and sensitivity of the three methods under routine conditions and achieved 96.0% concordance of p.T790M results. A limit of detection for mutation calling using digital PCR (>0.1%) and NGS (>0.2%) was established. In total, 62.5% of known primary EGFR mutations were successfully detected in cfDNA. In 56.0% of the patients with detectable EGFR primary mutations, we identified a resistance conferring the EGFR p.T790M mutation.