DNA extracted from FFPE specimens is usually degraded, and 21 FFPE samples of mutationCnegative NSCLC were used to assign cutoff ideals. and the results were reported to physicians within 14 days. TKI-sensitizing and T790M mutations were recognized in plasma of 120 (46.2%) and 75 (28.8%) individuals, respectively. T790M was recognized in 56.7% of individuals with plasma positive for TKI-sensitizing mutations. For the 41 individuals with paired samples acquired after acquisition of EGFR-TKI resistance, the concordance for mutation detection by ddPCR in plasma compared with tumor cells or malignant fluid specimens was 78.0% for TKI-sensitizing mutations and 65.9% for T790M. Conclusions Noninvasive genotyping by ddPCR with cell-free DNA extracted from plasma is definitely a promising approach to the detection of gene mutations during targeted treatment. amplification, overexpression of hepatocyte growth element, and activation of the insulin-like growth element 1 receptorhave been recognized. The T790M mutation of is the most common cause of acquired resistance to EGFR-TKIs, becoming found in up to 50% of individuals treated with these medicines [7C10], and several next-generation EGFR-TKIs, such as CO-1686 and AZD9291 (irreversible T790M mutantCspecific EGFR-TKI with little inhibitory activity Montelukast sodium for wild-type EGFR), have been developed to overcome such resistance [11C13]. However, the overall performance of a second biopsy to assess T790M mutation status can be problematic depending on the size and location of the tumor cells, probably requiring invasive methods such as mediastinoscopy or video-assisted thoracoscopy. Liquid biopsy, a noninvasive means to detect malignancy cell DNA in blood, has the potential to allow detection of malignancy, measurement of tumor burden, and evaluation of drug level of sensitivity or resistance. In the present study, we prospectively examined whether droplet digital polymerase chain reaction (ddPCR) analysis of cell-free DNA (cfDNA) might allow highly specific and quantitative assessment of TKI-sensitizing and T790M resistance mutations of in individuals with advanced NSCLC who acquire resistance to EGFR-TKI therapy. RESULTS Cutoff ideals for prescreening To optimize the specificity of our GLCE genotyping assays, we identified the cutoff ideals for plasma cfDNA, pleural effusion or ascites fluid, and formalin-fixed, paraffin-embedded (FFPE) specimens with plasma cfDNA derived from 10 healthy volunteers, normal genomic DNA (Promega, Madison, WI), and mutationCnegative FFPE samples. No background noise (0 copies per reaction) was recognized for assay of harboring T790M, L858R, E746-A750del, L861Q, or G719X mutations with plasma cfDNA derived from each of the 10 healthy volunteers or with the normal genomic DNA. The cutoff value for each mutation was consequently arranged at 3 copies per reaction (20 L), or 0.15 copies/L, for plasma cfDNA. The DNA extracted from pleural effusion or ascites fluid was of high molecular weight related to that isolated from blood plasma. The same cutoff value was consequently selected for these specimens. DNA extracted from FFPE specimens is usually degraded, and 21 FFPE samples of mutationCnegative NSCLC were used to assign cutoff ideals. The mean SD ideals for T790M, L858R, E746-A750del, L861Q, and G719X mutant copy quantity in these 21 samples were determined, and the higher value of the mean + 3SD copy quantity or 3 copies per reaction was chosen as the cutoff for each mutation, consistent with the approach adopted inside a earlier study . The cutoff ideals were therefore arranged at 1.11 copies/L for T790M, 0.2 copies/L for L858R, 0.3 copies/L for E746-A750del, 0.15 copies/L for L861Q, and 1.8 copies/L for G719X. Patient characteristics We recruited 260 individuals with mutationCpositive NSCLC and acquired resistance to EGFR-TKIs from 29 organizations Montelukast sodium in Japan between 4 November 2014 and 13 March 2015 (Table ?(Table1).1). The subjects included 182 (70.0%) ladies and 186 (71.5%) never-smokers, with an overall median age of 68 years (range, 36 to 90). Most patients experienced disease of stage IIIb or IV at analysis (78.8%) and an Eastern Cooperative Oncology Group (ECOG) overall performance status of 0 to 2 (95.8%), and 191 (73.5%) received EGFR-TKI treatment as first-line therapy. With regard to the type of mutation recognized by commercial assays with diagnostic FFPE Montelukast sodium samples, 127 (48.8%) individuals had a deletion in exon 19, 122 (46.9%) experienced a missense mutation in exon 21 (L858R or L861Q), and 4 (1.5%) had a G719X mutation in exon 18. Most individuals (78.8%) were treated.