Treatment strategies and outcomes for patients with EGFR-mutant non-small cell lung cancer resistant to EGFR tyrosine kinase inhibitors: Focus on novel therapies.

Tyrosine kinase inhibitors (TKIs) are the standard of care for patients with non-small cell lung cancer (NSCLC) that harbor mutations of the epidermal growth factor receptor (EGFR) gene. First-line therapy for these patients is often osimertinib, a third-generation EGFR TKI. Erlotinib, gefitinib, afatinib, and dacomitinib are first- and second-generation TKIs that are also available. However, almost all patients eventually develop disease progression due to TKI-acquired resistance. The mechanisms of resistance after TKI exposure often involve EGFR or its downstream pathways. While a frequently utilized strategy for combating acquired resistance to EGFR TKIs remains standard platinum-based chemotherapy, clinical investigation of promising novel agents targeting common resistance mechanisms such as MET, HER2, and HER3 is of increased interest. In this review, we discuss the mechanisms of resistance to TKIs in EGFR-mutant NSCLC, examine current treatment standards, and discuss novel developing therapies. Both EGFR-dependent (involving secondary mutations in EGFR) and EGFR-independent (mutations that bypass EGFR signaling and histologic transformation) resistance mechanisms are considered. Several novel treatment strategies are emerging to overcome these resistance mechanisms, as the understanding and identification of specific EGFR-TKI resistance mechanisms continues to improve. The treatments in development aim to target or bypass the mechanisms of resistance, including MET-, HER2-, and HER3-directed therapies. In patients with acquired TKI resistance, molecular profiling at the time of initial progression may help identify relevant mechanisms of resistance. Clinical trial participation is vital to continued investigation for EGFR-mutant NSCLC.