Impact of Tumor Suppressor Gene Co-Mutations on Differential Response to EGFR TKI Therapy in EGFR L858R and Exon 19 Deletion Lung Cancer

Background: In most studies, patients with EGFR L858R mutant non-small cell lung cancer (NSCLC) have a shorter duration of response to EGFR tyrosine kinase inhibitor (TKI) therapy than do patients with EGFR exon 19 deletion NSCLC. The role that co-mutations play in this observation is unknown. Methods: We performed a single-institution retrospective analysis of patients with EGFR-mutant NSCLC (exon 19 deletion or L858R mutation) who received frontline EGFR TKI for metastatic disease between 2014 and 2019, and who had STAMP next-generation sequencing (NGS), a 130-gene platform. Time to treatment failure (TTF) and overall survival were calculated using Cox models adjusted for age, race, and brain metastases. Co-mutations in key tumor suppressor genes (TP53, RB1, KEAP1, CDKN2A, or CTNNB1) were identified and their effects on outcomes were evaluated. Analyses were stratified according to receipt of osimertinib versus nonosimertinib as frontline EGFR TKI. Results: Of 137 patients, 72 (57%) had EGFR exon 19 deletions and 65 (43%) had EGFR L858R mutations. Median TTF and OS on frontline TKI was shorter for the L858R cohort versus the exon 19 deletion cohort in univariate analysis. In adjusted models, this difference persisted for TTF but was no longer significant for OS. The difference in TTF in L858R mutant tumors was driven by the presence of co-mutations in key tumor suppressor genes. Conclusion: Patients with metastatic NSCLC with mutations in EGFR L858R had shorter TTF on frontline TKI compared to patients with EGFR exon 19 deletions. Co-mutations in tumor suppressor genes may play an important role in the differential response to TKI therapy.