Resistance to osimertinib in advanced EGFR-mutated NSCLC: a prospective study of molecular genotyping on tissue and liquid biopsies

Abstract

Background: Resistance to osimertinib in advanced EGFR-mutated non-small cell lung cancer (NSCLC) constitutes a significant challenge for clinicians either in terms of molecular diagnosis and subsequent therapeutic implications.

Methods: This is a prospective single-centre study with the primary objective of characterising resistance mechanisms to osimertinib in advanced EGFR-mutated NSCLC patients treated both in first- and in second-line. Next-Generation Sequencing analysis was conducted on paired tissue biopsies and plasma samples. A concordance analysis between tissue and plasma was performed.

Results: Sixty-five advanced EGFR-mutated NSCLC patients treated with osimertinib in first- (n = 56) or in second-line (n = 9) were included. We managed to perform tissue and liquid biopsies in 65.5% and 89.7% of patients who experienced osimertinib progression, respectively. Acquired resistance mechanisms were identified in 80% of 25 patients with post-progression samples, with MET amplification (n = 8), EGFR C797S (n = 3), and SCLC transformation (n = 2) the most frequently identified. The mean concordance rates between tissue and plasma for the EGFR activating mutation and for the molecular resistance mechanisms were 87.5% and 22.7%, respectively.

Conclusions: Resistance to osimertinib demonstrated to be highly heterogeneous, with MET amplification the main mechanism. Plasma genotyping is a relevant complementary tool which might integrate tissue analysis for the study of resistance mechanisms.

Fig. 1. NGS study at baseline.

Genetic variants were filtered and listed based on the selection described in methods section. Co-alteration burden indicates the number of genetic variants in each sample, excluding EGFR activating mutation and EGFR T790M. Green box, EGFR activating mutation (del19, exon 19 deletion); red box, EGFR T790M resistance mutation (cohort 2); light blue box, single nucleotide variation (SNV); purple box, copy number variation (CNV); yellow box, concomitant presence of SNV and CNV; LB liquid biopsy.

Fig. 2. NGS study at PD.

Candidate acquired alterations with osimertinib are represented. The frequency of the molecular alterations is shown in the right column. In case an alteration was found in both tissue and plasma, it was counted only once. Variants which appeared also at baseline were not represented. Green box, EGFR activating mutation (del19, exon 19 deletion); red box, EGFR T790M resistance mutation (cohort 2); light blue box, single nucleotide variation (SNV); purple box, copy number variation (CNV); yellow box, concomitant presence of SNV and CNV; pink box, fusion; T Tissue, LB liquid biopsy, orange box, primary resistance; white box, acquired resistance; ns non-shedder; exclamation point, increased alteration from baseline; ins20, exon 20 insertion.

Fig. 3. Overall resistance mechanisms stratified according to patients.

Pie chart shows the main molecular setting of patients at the time of PD depicted by the putative molecular mechanism that drove the resistance. Both tissue and plasma results were considered for the representation. Other gene alterations refer to genetic variants for which there is no strong evidence to drive resistance to osimertinib to date and included EGFR amplification, SMAD4, APC and CTNNB1. a Overall study cohort; b patients progressed to osimertinib in first-line. Amp amplification, ex20ins exon 20 insertion, SCLC small cell lung cancer, TK receptor Tyrosin Kinase receptor.

Fig. 4. Concordance between Tissue and Plasma at PD.

Paired tissue and plasma samples were analysed to define the concordance rate between the two sources. The analysis was divided between the activating mutation and putative molecular mechanisms of resistance. amp amplification, Del19 exon 19 deletion, ins20 exon 20 insertion, SNV single nucleotide variations.