EGFR mutated lung cancer accounts for a significant subgroup of non-small-cell 
lung cancer (NSCLC). Over the last decade, multiple EGFR tyrosine kinase 
inhibitors (EGFR-TKIs) have been developed to target mutated EGFR. However, 
there is little information regarding mutation specific potency of EGFR-TKIs 
against various types of EGFR mutations. The purpose of this study is to 
establish an in vitro model to determine the "therapeutic window" of EGFR-TKIs 
against various types of EGFR mutations, including EGFR exon 20 insertion 
mutations. The potency of 1st (erlotinib), 2nd (afatinib) and 3rd (osimertinib 
and rociletinib) generation EGFR-TKIs was compared in vitro for human lung 
cancer cell lines and Ba/F3 cells, which exogenously express mutated or wild 
type EGFR. An in vitro model of mutation specificity was created by calculating 
the ratio of IC50 values between mutated and wild type EGFR. The in vitro model 
identified a wide therapeutic window of afatinib for exon 19 deletions and L858R 
and of osimertinib and rociletinib for T790M positive mutations. The results 
obtained with our models matched well with previously reported preclinical and 
clinical data. Interestingly, for EGFR exon 20 insertion mutations, most of 
which are known to be resistant to 1st and 2nd generation EGFR-TKIS, osimertinib 
was potent and presented a wide therapeutic window. To our knowledge, this is 
the first report that has identified the therapeutic window of osimertinib for 
EGFR exon 20 insertion mutations. In conclusion, this model will provide a 
preclinical rationale for proper selection of EGFR-TKIs against 
clinically-relevant EGFR mutations.