STX-721 is an orally active, irreversible, covalent EGFR exon 20 insertion (ex20ins) inhibitor that selectively targets ex20ins-mutant dynamic protein states. STX-721 potently inhibits the kinase activity of EGFR ex20ins mutants (NPG, ASV, SVD) . STX-721 inhibits phosphorylation of EGFR (pEGFR Y1068) and downstream ERK (pERK Thr202/Tyr204), and suppresses proliferation of ex20ins-mutant Ba/F3 cells and human NSCLC cell lines (NCI-H2073 ASV KI, CUTO-14 ASV) . STX-721 induces tumor regression in EGFR ex20ins-mutant PDX/CDX models. STX-721 can be used for the study of non-small cell lung cancer (NSCLC) harboring EGFR or HER2 ex20ins mutations[1][2].