Efficacy of Icotinib, an EGFR Tyrosine Kinase Inhibitor in Non-Small Cell Lung Cancer Patients with Exon 19 Deletion and Exon 21 L858R: A Retrospective Analysis in China

<b><i>Introduction:</i></b> The effect of icotinib on non-small cell lung cancer (NSCLC) patients with <i>EGFR</i> exon 19 deletions (19-Del) or L858R point mutation in exon 21 (21-L858R) remains inconsistent. This study aimed to evaluate the efficacy and safety of icotinib in patients with advanced NSCLC harboring these 2 <i>EGFR</i> mutations. <b><i>Methods:</i></b> We retrospectively assessed the clinical effects of first-line icotinib on advanced NSCLC patients with 2 classic <i>EGFR</i> mutations. Kinase activity assays were used to reaffirm the preclinical efficacy. <b><i>Results:</i></b> Among 2,757 patients, 2,365 (86%) harbored 19-Del (1,346/2,757, 49%) or 21-L858R (1,019/2,757, 37%) mutation. Patients with 19-Del had a higher response rate (ORR; 67.8 vs. 62.1%; <i>p</i> = 0.0039) and disease control rate (98.5 vs. 97.2%; <i>p</i> = 0.0223) than those with 21-L858R mutation. The median progression-free survival (PFS) in the 19-Del group (22.3 months, 95% confidence interval [CI]: 21.3–23.4) was significantly longer than that in the 21-L858R group (20.4 months, 95% CI: 19.5–21.7) (<i>p</i> = 0.004). In multivariate analysis, mutation types, clinical stage, and smoking history were significant factors for PFS. Additionally, an in vitro study indicated the 50% inhibitory concentrations (IC₅₀) of icotinib was lower for <i>EGFR</i> 19-Del than 21-L858R. <b><i>Conclusion:</i></b> These results suggest that <i>EGFR</i> 19-Del confers superior PFS and response to the icotinib treatment compared to 21-L858R.