Analysis of EGFR mutation status in tissue and plasma for predicting response to EGFR-TKIs in advanced non-small-cell lung cancer

The detection of mutations in the epidermal growth factor receptor (EGFR) gene in tumor tissues has been established as the gold standard for predicting the efficacy of treatment with EGFR-tyrosine kinase inhibitors (EGFR-TKIs) in advanced non-small-cell lung cancer (NSCLC). The current study aimed to investigate whether the presence of co-existing EGFR mutations in tumor tissue and in cell-free tumor DNA (ctDNA) in the plasma predicts a more favorable outcome of EGFR-TKI treatment in advanced NSCLC. A total of 287 NSCLC patients who had undergone EGFR-TKI treatment were enrolled and stratified into four subgroups: Wild-type EGFR in plasma and tissue specimens (B-/T-); mutated EGFR in plasma and tissue specimens (B+/T+); mutated EGFR in only in plasma samples (B+/T-); or mutated EGFR in only tissue specimens (B-/T+). EGFR mutations were tested using denaturing high-performance liquid chromatography and confirmed by amplification-refractory mutation system analysis. Of the 287 patients, 101 had mutations in both tissue and plasma samples and 103 had mutation in either tissue (n=65) or plasma (n=38). The median progression-free survival (mPFS) times were 9.2 and 2.0 months in the B+/T+ and B-/T- groups, respectively. The mPFS times were 7.9 months in the B-/T+ group and 11.9 months in the B+/T- group (P=0.001). Among the 187 patients with available pre-EGFR-TKI plasma samples, 70 received first-line EGFR-TKI treatment, and the mPFS in the B+/T+ group was longer than in the B-/T+ or B+/Tgroups (18.8 vs. 9.4 vs. 6.9 months; P=0.003). In second-line setting of EGFR-TKI therapy, the groups of patients with EGFR mutation in ctDNA, regardless of the mutation status in the tissues, exhibited longer mPFS times compared with the B-/T+ group (10.0 vs. 5.8 months; P=0.044). The results suggest that co-existence of EGFR mutations in tissue and ctDNA predict longer PFS times for NSCLC patients who receive first-line EGFR-TKI therapy. In addition, real-time detection in ctDNA is an excellent predictor for the efficacy of second-or higher line EGFR-TKI therapy.