EGFR and non-small cell lung carcinoma: In the present study, we examined the relationship between T790M mutation and clinicopathologic or prognostic factors in patients showing relapse of EGFR-mutant NSCLC after 1st or 2nd EGFR-TKI therapy, and our data showed that a high proportion of patients with EGFR deletion 19 mutation who received long-term 1st or 2nd EGFR-TKI therapy demonstrated a high prevalence of T790M mutation.