Comprehensive Analysis of the Discordance of EGFR Mutation Status between Tumor Tissues and Matched Circulating Tumor DNA in Advanced Non-Small Cell Lung Cancer

Abstract

Introduction: This study aimed to address the underlying reasons for and clinical significance of the discordant EGFR mutation (EGFRm) status between tumor tissue (TT) and circulating tumor DNA (ctDNA).

Methods: Three groups of EGFR tyrosine kinase inhibitor (EGFR TKI)-treated patients whose EGFRm status was determined by the amplification refractory mutation system (ARMS) were included (group A, TT-positive/ctDNA-positive EGFRm status; group B, TT-negative/ctDNA-positive EGFRm status; and group C, TT-positive/ctDNA-negative EGFRm status). Patients with discordant EGFRm status were reevaluated by droplet digital polymerase chain reaction (ddPCR) and next-generation sequencing. Meanwhile, surgical tumor specimens were microdissected for EGFRm detection by ddPCR.

Results: Of the 2463 patients with matched TT and ctDNA specimens, 1017 patients carried EGFRm in TT and/or ctDNA by the ARMS. Of these 1017 patients, 472 received EGFR TKIs, including 264, 28, and 180 in groups A, B, and C, respectively. The median progression-free survivals of those receiving EGFR TKIs across the three groups were similar (p = 0.062). Through ddPCR and next-generation sequencing of biopsy specimens (n = 22) and microdissected surgical specimens (n = 5), 27 patients in group B were identified as harboring EGFRm. After reevaluation by ddPCR, 64 patients in group C tested positive for EGFRm in their ctDNA. ctDNA as a screen for EGFRm then tissues as supplement (ctDNA→TT pattern) had similar detection efficiency and saved about 30% of TT compared with TT for initial EGFRm detection followed by ctDNA (TT→ctDNA pattern).

Conclusions: Intratumor heterogeneity and the relatively low sensitivity of the ARMS contributed to discordant EGFRm status between TT specimens and ctDNA. The ctDNA→TT pattern might be a rational clinical procedure for EGFRm determination.

Keywords: Circulating tumor DNA; Discordance of mutation; Epidermal growth factor receptor mutation; Heterogeneity; Non–small cell lung cancer.