In this study, we examined whether the selective KOR agonist U50,488H could inhibit the growth of gefitinib-sensitive and EGFR mutant (delE746-A750, L858R) NSCLC cells (HCC827) and gefitinib-resistant and EGFR mutant (T790M) NSCLC cells (H1975), and investigated the signalling mechanism of the KOR-mediated inhibitory effect on tumour cell growth. This evidence concerns the gene EGFR and neoplasm.