Monitoring of circulating tumor DNA in non-small cell lung cancer patients treated with EGFR-inhibitors.

Abstract

11535 Background: Epidermal growth factor receptor (EGFR) inhibitors such as erlotinib and gefitinib are routinely used in the treatment of non-small cell lung cancer (NSCLC). Monitoring of EGFR mutations in circulating tumor DNA (ctDNA) derived from plasma has been proposed as an alternative for repeated tumor biopsies. Our aim was to investigate the dynamics of ctDNA in a cohort of NSCLC patients and explore the roles of EGFR driver and resistance mutations in predicting disease progression and progression free survival (PFS). Methods: NSCLC patients treated with either erlotinib or gefitinib as first-line anti-EGFR therapy were included. Clinical data was collected retrospectively from medical records. Plasma samples collected as part of routine care were analyzed. First DNA was isolated from plasma using the QIAsymphony SP (Qiagen). Then EGFR driver (L858R and exon 19 deletions) and resistance (T790M) mutations were quantified using the X100 Droplet Digital PCR and analyzed using QuantaSoft software (Bio-Rad). The dynamics of ctDNA mutations over time and the relationship between copy numbers and progression free survival were explored. Results: 68 NSCLC patients and 249 plasma samples (1-13 per patient) were included in the analysis. In 33 patients, the T790M mutation was detected. The median (range) T790M concentration in these samples was of 7.3 (5.1 - 3688.7) copies/mL. In 30 patients, the L858R or exon 19 deletion driver mutations were found in median concentrations of 11.7 (5.1 – 12393.3) and 27.9 (5.9 – 2896.7) copies/mL, respectively. Using local polynomial regression, the copies/mL of EGFR driver mutations increased several weeks prior to progression on standard response evaluation. In Kaplan-Meier analysis, patients with a detectable T790M mutation during the first 8 weeks of treatment had a shorter PFS (7.6 versus 14.4 months, p < 0.01, log-rank test). Conclusions: Early detection of the T790M mutation in plasma ctDNA is related to poor PFS. Furthermore, an increase in the copies/mL of the EGFR driver mutation over time may predict clinical progression.