Competitive evolution of NSCLC tumor clones and the drug resistance mechanism of first-generation EGFR-TKIs in Chinese NSCLC patients

Although many studies have reported on the resistance mechanism of first-generation EGFR TKIs (1st EGFR TKIs) treatment, large-scale dynamic ctDNA mutation analysis based on liquid biopsy for non-small cell lung cancer (NSCLC) in the Chinese population is rare. Using in-depth integration and analysis of ctDNA genomic mutation data and clinical data at multiple time points during the treatment of 53 NSCLC patients, we described the resistance mechanisms of 1st EGFR TKIs treatment more comprehensively and dynamically. The resulting profile of the polyclonal competitive evolution of the tumor provides some new insights into the precise treatment of NSCLC. A prospective study was conducted in patients with advanced NSCLC with acquired resistance to erlotinib, gefitinib or icotinib. By liquid biopsy, we detected mutations in 124 tumor-associated genes in the context of drug resistance. These 124 genes covered all tumor therapeutic targets and related biological pathways. During the entire course of treatment, the interval between two liquid biopsies was two months. Unlike the common mutations tested in tissue samples, our data showed a higher coverage of tumor heterogeneity (32.65%), more complex patterns of resistance and some new resistance mutation sites, such as EGFR p.V769M and KRAS p.A11V. The major resistance-associated mutations detected were still EGFR p.T790M (45.28%), other point mutations in EGFR (33.9%), and KRAS and NRAS mutations (15.09%). These mutation ratios might be considered as a preliminary summary of the characteristics of Chinese patients. In addition, starting from the two baseline mutations of the EGFR gene (19del vs. L858R), we first described the detailed mutation profile of the EGFR gene. Although there was no significant difference in the number of patients with EGFR p.19del and EGFR p.L858R baseline mutations (24% vs. 16%, P = 0.15), patients from the EGFR p.19del baseline group were much more likely to develop EGFR p.T790M resistance mutations (62.1% vs. 19.3%, P = 0.007). Through careful integration of gene mutation information and clinical phenotype information, an interesting phenomenon was found. Although the variant allele fraction (VAF) of the EGFR p.T790M mutation was significantly linearly correlated with that of the EGFR drug-sensitive mutation (r = 0.68, P = 0.00025), neither VAF was associated with the tumor volume at the advanced stage. It was shown that other tumor clones might contribute more to the resistance to 1s