Sensitivity To Egfr Inhibitors Based On Location Of Egfr Exon 20 Insertion Mutations Within The Tyrosine Kinase Domain Of Egfr.

7523 Background: Epidermal growth factor receptor (EGFR) mutations (M) define an important subgroup of non-small-cell lung cancer (NSCLC). Most patients whose tumors harbor exon 19 deletions or L858R EGFR M have responses to reversible ATP-mimetic EGFR tyrosine kinase inhibitors (TKIs), gefitinib and erlotinib. Exon 20 insertion M comprise ~5% of EGFR M, occur at the N-lobe of EGFR after its C-helix (AA M766), and nearly all NSCLCs with EGFR exon 20 insertion M display lack of responses to EGFR TKIs (Yasuda H. Lancet Oncol 2011). Methods: We have 1) compiled genotype-clinical outcomes of EGFR exon 20 insertion M NSCLCs to EGFR TKIs, 2) generated a comprehensive panel of exon 20 EGFR M constructs using site-directed mutagenesis and introduced them into Ba/F3 cells for in vitro analysis, and 3) compared NSCLC cell lines with EGFR M to a novel malignant pleural effusion-derived cell line. Results: The disease control rate of gefitinib or erlotinib was significantly higher in EGFR exon 20 insertion M located within the C-helix (3/3,100%) when compared to M following the C-helix (1/14, 7%; p=0.00059). The NSCLC with EGFR-A763_Y764insFQEA (located within the C-helix of EGFR) achieved a partial response to erlotinib that lasted 18 months. Most other exon 20 insertion M-positive NSCLCs did not respond (p=0.07). Eight representative exon 20 insertion M were studied (including EGFR-A763_Y764insFQEA, Y764_S765insHH, A767_V769dupASV, D770_N771insNPG, H773_V774insH). All, but A763_Y764insFQEA, were resistant to micromolar concentrations (C) of EGFR TKIs. Ba/F3 cells with EGFR-A763_Y764insFQEA underwent apoptosis upon exposure to nanomolar C of erlotinib. A patient-derived cell line with EGFR-A763_Y764insFQEA had phosphorylated EGFR, ERK and AKT inhibited by nanomolar C of erlotinib. Conclusions: Not all EGFR exon 20 insertion mutations are resistant to EGFR TKIs, and in specific EGFR-A763_Y764insFQEA is an EGFR TKI-sensitive M. This finding has clinical implications for the care of the 10,000 cases of EGFR exon 20 insertion M NSCLC diagnosed yearly and points towards the need to define the molecular mechanisms that underlie differential responses to EGFR TKIs.