Application of a Highly Sensitive Detection System for Epidermal Growth Factor Receptor Mutations in Plasma DNA

Introduction: Detection of epidermal growth factor receptor (EGFR) mutations is indispensable to determine an appropriate lung cancer treatment. Although retreatment often prolongs survival, how to select the appropriate population for retreatment has not been clarified. Methods: We used novel methods to identify EGFR mutations: wild inhibiting polymerase chain reaction (PCR) and quenched probe system (WIP-QP) for exon 19 deletions and mutation-biased PCR and quenched probe system for L858R. After the detection limits were determined, we examined DNA isolated from lung cancer specimens and circulating plasma DNA samples of 39 adenocarcinoma patients whose primary tumors harbored EGFR exon 19 deletions or L858R. Results: Detection limit was 0.005 to 0.04 ng in genomic DNA and 0.1% to 0.3% in mutant plasmids. The results of cancer tissue specimens were identical to those with existing systems (nucleic acid-locked nucleic acid PCR clamp or cycleave PCR), except for two samples that showed both exon 19 deletions and L858R. One of the two samples was confirmed to harbor L858R mutation by allele-specific oligonucleotide PCR; the other one did not. Exon 19 deletions and L858R were detected in 44.7% and 8.7% of patients, using plasma DNA, among those who carried the identical abnormalities in primary tumors all of cases that evidenced pathological stage IV except for one patient, suggesting that EGFR mutations might be preferentially detected in plasma DNA obtained from patients in advanced stages. Serial monitoring of these mutations with T790M, a gate keeper mutation, demonstrated correlation with disease state. Conclusions: Our novel detection systems for EGFR mutations could be useful not only at the beginning of treatment but also for monitoring using plasma DNA for deciding appropriate treatment, including rechallenge with EGFR-tyrosine kinase inhibitors.