Strategies for treating patients with EGFR-TKI resistance using next-generation EGFR-TKIs or other drugs are being actively discussed and tested in clinical trials [40]. mutations. Also, 7 (44%) were positive for the T790M mutation, with fractions of T790M (+) cfDNA ranging from 7.4% to 97%. T790M positivity in cfDNA was consistent in eight IL24 of ten patients for whom rebiopsied tumor tissues were analyzed, whereas the remaining cases were negative in cfDNA and positive in rebiopsied tumors. Prior to EGFR-TKI therapy, cfDNAs from 9 (38%) and 0 of 24 Bleomycin patients were positive for TKI-sensitive and T790M mutations, respectively. Next-generation sequencing of cfDNA from one patient who exhibited innate resistance to TKI despite a high fraction of TKI-sensitive Bleomycin mutations and the absence of the T790M mutation in his cfDNA revealed the presence of the L747P mutation, a known driver of TKI resistance. Conclusion. Picoliter-ddPCR examination of cfDNA, supported by next-generation sequencing analysis, enables noninvasive assessment of mutations that confer resistance to TKIs. Implications for Practice: Noninvasive monitoring of the predominance of tumors harboring the secondary T790M mutation in the activating mutation in gene is necessary for precise and effective treatment of lung adenocarcinoma. Because cells harboring the T790M mutation are resistant to epidermal growth factor receptor-tyrosine-kinase inhibitors (TKIs), the predominance of tumor cells harboring the T790M mutations influences the choice of whether to use conventional or next-generation TKIs. Digital polymerase chain reaction-based examination of cfDNA is a promising method; however, its feasibility, including its consistency with examination of rebiopsied tumor tissue, has not been fully proven. Here, picoliter-droplet digital polymerase chain reaction technology is presented as a candidate method for testing cfDNA and assessing the predominance of T790M-mutant tumors. (epidermal growth factor receptor) is a driver gene of non-small cell lung cancer (NSCLC), particularly lung adenocarcinoma (LADC). Activating somatic mutations in this gene define a subset of cases that respond to specific EGFR-tyrosine-kinase inhibitors (TKIs) such as gefitinib and erlotinib [1, 2]. The most frequent mutations in occur in the exons encoding the kinase domain of EGFR, including various types of in-frame deletions in exon 19 (19del) and a point mutation in exon 21 leading to the Bleomycin substitution of leucine for arginine at position 858 (L858R). Tumors harboring these TKI-sensitive mutations nearly always acquire resistance to TKIs within 2 years [3, 4]. The most common mechanism of resistance, accounting for 60% of cases, is the occurrence of the secondary mutation T790M (replacing a gatekeeper amino acid) in the allele harboring the TKI-sensitive mutation [5]. To overcome resistance to conventional EGFR-TKIs, a new generation of drugs (including AZD9291, CO-1686, and HM61713) that suppress the kinase activity of EGFR proteins harboring secondary T790M substitutions is currently being developed [6C9]. Phase I clinical trials demonstrate that progressed NSCLC patients who are diagnosed with T790M-positive tumors by genetic testing of rebiopsied tumor tissues respond to these new drugs [10]. However, because the new drugs bind their targets irreversibly, they are associated with severe side effects that are not observed during conventional EGFR-TKI therapy. In addition, other mutations in EGFR also confer resistance [11]. Therefore, to achieve precise and effective treatment of mutation-positive NSCLC patients, it is necessary to monitor the predominance of mutations that confer TKI resistance during therapy; the choice between conventional and next-generation EGFR-TKIs must be made based on the identities of the mutations conferring TKI resistance [6, 7]. Bleomycin Circulating plasma cell-free DNA (cfDNA), which is released into plasma from tumor tissues or circulating tumor cells (CTCs), represents a promising source of material for noninvasive liquid biopsy that could provide genetic information about CTCs and residual tumor cells Bleomycin [12C14]. cfDNA is particularly attractive for use in the lung cancer clinic due to the occasional difficulty of obtaining tumor tissues with high cellularity [15, 16]. Indeed, mutations present in tumor cells can be detected in the cfDNA of NSCLC.
