B-120 Incremental Diagnostic Yield of Next-Generation Sequencing in NSCLC with Wild-Type Results by cobas EGFR Testing and Characterization of Rare EGFR L833V Mutation

Abstract

EGFR mutation testing is essential for therapeutic decision-making in non–small cell lung cancer (NSCLC). Routine assays primarily detect common EGFR alterations, such as exon 19 deletions and L858R substitutions, but may fail to identify rare or non-classical variants. At National Taiwan University Hospital (NTUH), the EGFR positivity rate determined by cobas EGFR testing was 61.12% over the past seven years. This study evaluated the incremental diagnostic yield of next-generation sequencing (NGS) in NSCLC cases with wild-type results by cobas EGFR testing and characterized the clinicopathological features of the rare EGFR L833V mutation. NGS-based comprehensive genomic profiling was performed in NSCLC cases that were wild-type by cobas EGFR testing and ALK IHC–negative. In addition, a retrospective review of an institutional NGS database comprising 819 NSCLC patients was conducted to identify cases harboring EGFR L833V mutations. Molecular profiles, clinical characteristics, and treatment outcomes were analyzed. Among 138 evaluable NSCLC cases with wild-type results by cobas EGFR testing and negative ALK IHC, NGS identified reportable genomic alterations in 68 cases (49.3%). EGFR alterations were detected in 13 cases (9.4%), including classical mutations (3.6%) and non-classical mutations (5.8%); EGFR amplification was observed in 2.9%. Non-EGFR actionable alterations (approximately 40%) included BRAF V600E, ERBB2 alterations, KRAS G12C, MET amplification or exon 14 skipping, and RET or ROS1 fusions. Retrospective analysis identified 12 cases harboring EGFR L833V mutations, frequently co-occurring with H835L, with treatment responses observed across first-, second-, and third-generation EGFR tyrosine kinase inhibitors. NGS substantially enhances detection of actionable genomic alterations in NSCLC cases with wild-type results by cobas EGFR testing and enables identification of rare EGFR variants such as L833V. Integration of NGS into routine molecular diagnostics may optimize precision oncology in this population.