Tumor heterogeneity turns out to be one of the key mechanisms underlying resistance to EGFR-targeted therapies.17-19,21-28 In this study, we analyzed pretreatment and post-treatment biopsy samples and clinical features of patients with NSCLC treated with third-generation EGFR inhibitors to assess determinants of IR and AR. The gene discussed is EGFR; the disease is neoplasm.