Changes in the concentration of EGFR-mutated plasma DNA in the first hours of anti-EGFR therapy allow the prediction of tumor response in patients with EGFR-driven lung cancer

Abstract

This study aimed to analyze changes in the plasma concentration of EGFR-mutated DNA occurring immediately after the start of therapy with EGFR tyrosine kinase inhibitors (TKIs). The study included 30 patients with EGFR mutation-driven non-small cell lung cancer (NSCLC). Serial plasma samples were collected before intake of the first tablet and at 0.5, 1, 2, 3, 6, 12, 24, 36 and 48 hours after the start of the therapy. EGFR-mutated plasma DNA (EGFR+ ctDNA) was detectable at diagnosis in 25 out of 30 study participants. There were different patterns of changes of the amount of circulating tumor DNA, i.e., the consistent decline of ctDNA content, or continuing increase of the number of circulating EGFR mutant copies, or alternating spikes and drops in the ctDNA concentration. Correlation with the disease outcome was observed only for the measurement performed at 48 hours. Twelve (50%) out of 24 informative patients showed >25% reduction of the ctDNA content at 48 h time point; all these patients demonstrated disease control after 4 and 8-12 weeks of therapy. The remaining 12 individuals showed either stable content of circulating EGFR+ DNA (n = 5) or the elevation of ctDNA concentration (n = 7). 10 of 12 patients with elevated or stable ctDNA level achieved an objective response at 4 weeks, but only 5 of 10 evaluable patients still demonstrated disease control at 8-12 weeks (p = 0.014, when compared to the group with ctDNA decrease). The decline of the amount of circulating EGFR mutant copies also correlated with longer progression-free survival (PFS; 14.7 months vs. 8.5 months, p = 0.013). Conclusion: Monitoring of plasma EGFR-M+ concentration within the first hours of the TKI therapy may be used as an immediate predictor of tumor response to the treatment.