e19046 Background: Detection of EGFR alterations is critical for predicting the response to tyrosine kinase inhibitors (TKI) in patients with non-small-cell lung cancer (NSCLC). In clinical practice, molecular testing is performed on tumor tissues when available. We investigated the use of circulating cell-free DNA for the detection of EGFR alterations in patients with NSCLC. Methods: Serum and plasma were obtained by centrifugation (10 min, 2,000 g, 20°C) performed within 3 hours following blood collection. Cell-free DNA was extracted using the QIAamp Circulating Nucleic Acid kit (Qiagen). Detection of EGFR alterations was performed using the approved Therascreen EGFR RGQ kit (Qiagen). Samples were tested positive for EGFR mutation when the ΔCt value (Ct of the mutation specific PCR – Ct of the control PCR) was lower than 12 for exon 19 deletions, and below 14 for L858R mutation. Results: No EGFR alteration was detected in samples collected from healthy donors (n=6), NSCLC patients with a wild type EGFR (n=60), and early stages NSCLC patients presenting an EGFR mutation in their tumor (n=11). Thirteen metastatic patients presenting an EGFR mutation in their tumor were tested before initiation of TKI treatment. When available, both serum and plasma were analyzed. Nine of these patients (9/13; 69.2%) were tested positive in their serum. The ΔCt values obtained were lower for plasma than for serum in most cases, and more patients (10/11; 90.9%) were EGFR mutation positive when plasma was tested. Finally we tested 3 patients during TKI treatment on a monthly basis. For 2 patients we were unable to detect the mutation initially found in pretreatment samples. Clinically, both patients were partial responders. The third patient did not respond to TKI, and we detected the EGFR mutation with stable ΔCt values at all points tested. Conclusions: EGFR alterations can be found in patients presenting an EGFR mutation in a metastatic NSCLC. Plasma samples allowed a better detection rate. Our results suggest that DNA circulating in plasma is a useful alternative source of tumor DNA that could be used for determining EGFR mutation status, and for follow-up of treatment. Supported by a grant from Astra-Zeneca.
Monitoring EGFR C797S mutation in Japanese NSCLC patients with serial cell free DNA evaluation using digital droplet PCR