Analysis of the effect of baseline detection and early clearance of ct-DNA, on survival outcomes among patients with advanced EGFR-mutant non-small cell lung cancer.

Background: To determine if circulating tumor DNA (ct-DNA) dynamics of epidermal growth factor receptor (EGFR) mutation in plasma can identify a subset of patients with EGFR-mutant (EGFR- m) non-small cell lung cancer (NSCLC) with inferior survival outcomes, we analyzed and compared survival outcomes among patients with and without baseline presence and early clearance of EGFR ct-DNA in plasma.
Material and Methods: For 66 patients newly dia-gnosed with EGFR- m NSCLC, plasma samples were collected at baseline and 1st response assessment at 12-24 weeks for extraction of ct-DNA. Estimation of ct-DNA (EGFR exons 18, 19, 20 and 21) was done using droplet digital polymerase chain reaction (dd-PCR) on the QX200 ddPCR system (BioRad, USA). Patients with detectable EGFR ct-DNA at baseline (sample 1), with either undetectable or persistent detectable ct-DNA in sample 2 were classified as clearers and non-clearers, respectively.
Results: Fifty-three patients received 1st/ 2nd generation EGFR tyrosine kinase inhibitors (TKIs) and 13 received either 3rd generation TKI (osimertinib) or chemotherapy plus gefitinib. The baseline ct-DNA-positive group had more patients with extra thoracic disease (60.4 vs. 48.5%). For the entire cohort, there was no difference in median progression-free survival (PFS) among baseline ct-DNA-negative (13.57 months) vs. ct-DNA-positive patients (12.32 months) (HR 0.74). There was a significant improvement of PFS among early ct-DNA clearers vs. non-clearers (12.32 vs. 9.92 months; HR 0.57). For those treated with 1st/ 2nd generation EGFR TKIs, this improvement in median PFS among early ct-DNA clearers vs. non-clearers was more apparent (11.76 vs. 6.8 months; HR 0.34).
Conclusions: Baseline detection of the presence of ct-DNA of EGFR mutation in plasma was not predictive of first-line PFS, but is associated with extra thoracic disease. Patients with EGFR mutation and persistence of ct-DNA at first follow-up have worse PFS and overall survival (OS) in comparison to those clearing the same in plasma, especially among those treated with 1st/ 2nd generation EGFR TKIs.