LAUSR

EGFR exon 19 deletion (Del‐19) comprises multiple advanced NSCLC subtypes. EGFR‐tyrosine kinase inhibitor (TKI) efficacy and T790M acquisition in various Del‐19 subtypes is unknown. We prospectively collected tissue samples from patients harboring NSCLC with Del‐19 between 2006 and 2020. We evaluated EGFR‐TKI treatment effectiveness among the different Del‐19 subtypes. We collected 1391 NSCLC samples from 892 patients with Del‐19, and the most common subtype was del E746‐A750 (67.5%). 741 patients had taken first‐ or second‐generation EGFR‐TKIs. There were no significant differences in response rates between patients with different Del‐19 subtypes (P = .630). Patients with indel E746 had the longest median PFS (14.6 months), but those with non‐LRE deletions had the shortest PFS (8.9 months; P = .002). For OS analysis, patients with indel E746 also had the longest OS (34.1 months), but those with non‐LRE deletions had the shortest OS (21.1 months; P = .046). Patients with different Del‐19 subtypes showed no significant differences in the T790M acquisition rates (P = .443). Among the 151 patients with acquired T790M who received third‐generation EGFR‐TKIs, the Del‐19 subtype was not associated with different RR and PFS. In vitro cellular viability and activation of the EGFR pathway analysis were consistent with the clinical findings. In conclusion, compared with del E746‐A750, indel E746 was associated with longer PFS and OS, but the non‐LRE subtype was correlated with shorter survival prognosis. There were no significant differences in the acquired T790M rate and treatment effectiveness of subsequent third‐generation EGFR‐TKIs between various Del‐19 subgroups.