Concordance between Tissue- and Plasma-based EGFR Mutation Testing According to Testing Interval in Non-small Cell Lung Cancer

Testing for epidermal growth factor receptor (EGFR) mutations is essential for selecting targeted therapy in patients with non-small cell lung cancer (NSCLC).This study evaluated the concordance between tissue-and plasma-based EGFR mutation testing and its association with testing interval.We retrospectively reviewed 233 patients with NSCLC who underwent both tests between January 2024 and February 2026.Overall agreement, positive percent agreement (PPA), negative percent agreement (NPA), and Cohen's kappa coefficient (κ) were calculated.The overall agreement was 68.7% (95% confidence interval [CI], 62.5~74.3),with a κ value of 0.310 (95% CI, 0.213~0.407).The PPA and NPA were 29.4% and 99.2%, respectively.Concordance decreased as the testing interval increased, and discordant cases were more frequently associated with stage I~II disease.Using tissue-based testing as the reference, plasma-based EGFR testing showed high negative but relatively low positive agreement.Plasma EGFR testing may serve as a complementary approach when tissue sampling is infeasible or repeat molecular testing is required.Negative plasma results should be interpreted cautiously in patients with early-stage disease or low tumor burden.Disease stage and clinical factors should be considered when interpreting the relationship between testing interval and concordance.