Digital PCR analysis of plasma cell-free DNA for non-invasive detection of drug resistance mechanisms in EGFR mutant NSCLC: Correlation with paired tumor samples
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Hidenobu Ishii1, Koichi Azuma1, Kazuko Sakai2, Akihiko Kawahara3, Kazuhiko Yamada1, Takaaki Tokito1, Isamu Okamoto4, Kazuto Nishio2, Tomoaki Hoshino1
1Division of Respirology, Neurology, and Rheumatology, Department of Internal Medicine, Kurume University School of Medicine, Kurume, Fukuoka, Japan
2Department of Genome Biology, Kinki University Faculty of Medicine, Osaka, Japan
3Department of Diagnostic Pathology, Kurume University Hospital, Kurume, Fukuoka, Japan
4Center for Clinical and Translational Research, Kyusyu University Hospital, Fukuoka, Japan
Koichi Azuma, e-mail: firstname.lastname@example.org
Keywords: T790M mutation, cell-free DNA, digital PCR, EGFR, non-small-cell lung cancer
Received: May 20, 2015 Accepted: August 04, 2015 Published: August 17, 2015
As the development of resistance to epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors (TKIs) has become an issue of concern, identification of the mechanisms responsible has become an urgent priority. However, for research purposes, it is not easy to obtain tumor samples from patients with EGFR mutation-positive non-small-cell lung cancer (NSCLC) that has relapsed after treatment with EGFR-TKIs. Here, using digital PCR assay as an alternative and noninvasive method, we examined plasma and tumor samples from patients with relapsed NSCLC to establish the inter-relationships existing among T790M mutation, activating EGFR mutations, HER2 amplification, and MET amplification. Paired samples of tumor and blood were obtained from a total of 18 patients with NSCLC after they had developed resistance to EGFR-TKI treatment, and the mechanisms of resistance were analyzed by digital PCR. Digital PCR analysis of T790M mutation in plasma had a sensitivity of 81.8% and specificity of 85.7%, the overall concordance between plasma and tissue samples being 83.3%. MET gene copy number gain in tumor DNA was observed by digital PCR in three patients, of whom one exhibited positivity for MET amplification by FISH, whereas no patient demonstrated MET and HER2 copy number gain in plasma DNA. Digital PCR analysis of plasma is feasible and accurate for detection of T790M mutation in NSCLC that becomes resistant to treatment with EGFR-TKIs.
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