P3.02b-016 An Exploration Study of Mechanisms Underlying Primary Resistance to EGFR-TKIs in Patients Harboring TKI-Sensitive EGFR Mutations: Topic: EGFR Biomarkers

Abstract

Primary resistance to EGFR-TKIs was generally defined as disease progression in less than 3 months without any evidence of objective response. Although possible mechanisms have been investigated in several preclinical and retrospective studies, little is known about the molecular backgrounds of primary resistance. Random Sample of Cases was used to screen TKI-sensitive patients to match with the primary resistant patients on the basis of clinical characteristics (smoking history, EGFR mutations etc.). DNA was extracted from the tumor and their matched normal material. The paired-end whole exome sequencing (WES) of DNA was performed on the Illumina HiSeq 2500 sequencing platform. Totally, five patients exhibiting primary resistance to EGFR-TKIs were enrolled and each was randomly matched with one patient possessing TKI sensitivity (Table 1). The mean depth of the WES was 100x. The mean number of nonsynonymous SNV per sample was 195 (range 97 to 348) in TKI-resistant group versus 84 (range 60 to 101) in TKI-sensitive group (P=0.059). Consistent with the initial result of Sanger sequencing, all 10 patients were found with EGFR sensitizing mutations (exon 19 deletions or L858R point mutation in exon 21), but no T790M mutation; the resistance group present with a lower EGFR mutant allele frequency than the sensitive group. Next generation sequencing of TKI-resistant specimens detected KRAS amplification (CNtumor / CNnormal = 2.6) in one of five patients, and MET amplification (CNtumor / CNnormal = 2.3) in another one. The recurrent mutation genes included FAT4, RBM10, TANC2, ACAN, PPFIA2, UBR4, XIRP2 and PRAMEF1. Next-generation sequencing offers more complete genomic analysis to understand the mechanism of differential responses to EGFR-TKIs, which can lead to more precision therapy. KRAS amplification appears to be a newly mechanism underlying primary resistance to EGFR-TKIs in patients harboring TKI-sensitive EGFR mutations. However, it needs to be validated in a larger cohort.