Activating mutations in the epidermal growth factor receptor (EGFR) gene, particularly in the tyrosine kinase domain, occur in approximately 20% of non-small cell lung cancer (NSCLC) cases. These mutations, commonly found as deletions in exon 19 or the L858R mutation in exon 21, are crucial targets for EGFR tyrosine kinase inhibitors (TKIs). The third-generation EGFR TKI, osimertinib (TAGRISSO; AstraZeneca, UK), is effective against tumors with the T790M mutation and a liquid biopsy test has been approved by the US Food and Drug Administration as a companion diagnostic for TAGRISSO. This test is now widely implemented in various countries, including South Korea. To ensure high-quality testing, the Korean Association of External Quality Assessment Service launched a liquid biopsy EGFR proficiency testing program in 2017. This study analyzed the results of this program for 2017–2023. The number of participating laboratories increased from three in 2017 to 30 in 2023. All participating laboratories reported results using the Cobas z 480 analyzer (Roche Diagnostics, Germany). The accuracy of the test results was high with 100% correctness in several trials. However, errors were reported in some trials with false positives (e.g., detecting mutations in mutation-free samples) being more common than false negatives. This study evaluated Korean clinical laboratory performance when undertaking liquid biopsies for EGFR mutations. Continuous participation in the external quality assessment program helps laboratories maintain and improve the quality of liquid biopsy EGFR testing, ultimately benefiting patient care by ensuring accurate and reliable mutation detection.

Keywords: Circulating tumor DNA, Epidermal growth factor receptor, Laboratory proficiency testing, Liquid biopsy