Preferential Sensitivity of the EGFR L858M/L861R Mutation to Second-Generation EGFR Tyrosine Kinase Inhibitors in Non-Small Cell Lung Cancer.

Purpose: Non-small cell lung cancer (NSCLC) frequently harbors targetable epidermal growth factor receptor (EGFR) mutations. However, rare variants such as EGFR L858M or L861R remain poorly characterized. This study aimed to elucidate the oncogenic potential and EGFR tyrosine kinase inhibitors (TKIs) sensitivity of the EGFR L858M/L861R mutation to inform personalized treatment strategies. Materials and Methods: Tumor samples from an NSCLC patient were analyzed using targeted panel sequencing and confirmed with the FoundationOne Liquid CDx assay. EGFR-mutant constructs, including L858M, L858R, L861R, L861Q, L858M/L861R, and L858R/L861Q, were generated and transduced into various cell lines. Cell viability, immunoblot, and soft agar colony formation assays were conducted to assess the oncogenicity and drug sensitivity, while computational protein modeling and docking simulations evaluated the drug-binding affinities of EGFR-TKIs. Results: Ba/F3 cells expressing the EGFR L858M/L861R mutation exhibited robust interleukin-3-independent proliferation accompanied by markedly increased EGFR phosphorylation, while NIH-3T3 cells showed anchorage-independent colony formation. Compared to other mutations, cells expressing EGFR L858M/L861R mutation were less sensitive to first-generation EGFR-TKIs (gefitinib, erlotinib) and third-generation EGFR-TKIs (osimertinib, lazertinib), whereas second-generation EGFR-TKIs (afatinib, poziotinib) demonstrated potent inhibitory effects. Computational modeling revealed a narrower drug-binding efficiency of first-generation inhibitors. Conclusion: The EGFR L858M/L861R mutation drives strong oncogenic signaling and exhibits preferential sensitivity to second-generation EGFR-TKIs. These findings underscore the importance of accurate molecular diagnosis for guiding effective, personalized therapeutic strategies in NSCLC.