Methods We evaluated the inhibitory effects of DS-2087b and poziotinib, an investigational tyrosine kinase inhibitor against Ba/F3 cells harboring WT EGFR and against EGFR/HER2 ex20ins mutations, including EGFR V769_D770 insertion ASV (EGFR ins.ASV); EGFR D770_N771 insertion SVD (EGFR ins.SVD); and HER2 A775_G776 insertion YVMA (HER2 ins.YVMA). Legal entity responsible for the study: Yuki Abe. Funding: Daiichi Sankyo Company, Limited.