Abstract 1598: EGFR mutational detection in vortex-enriched CTCs, ctDNA, and comparison to tumor tissue in non-small cell lung cancer (NSCLC) patients

Background Lung cancer is the leading cause of cancer-related mortality worldwide and 85% cases are NSCLC. Epidermal growth factor receptor (EGFR) mutations occur in 10-30% of NSCLC patients1. EGFR tyrosine kinase inhibitor (TKI) therapies, based on the evaluation of EGFR mutation, have shown dramatic clinical benefits. EGFR assays are mainly performed on tumor biopsies, which carry risks and expense and are not always successful1. In order to identify the development of secondary EGFR mutations, which cause resistance to 1st and 2nd generation TKI's and an indication for therapy with a 3rd generation drug, effective and non-invasive monitoring is needed. Liquid biopsies containing circulating tumor cells (CTCs) and circulating tumor DNA (ctDNA), allow such monitoring over the course of the therapy2. The Vortex Biosciences' VTX-1 Liquid Biopsy System enables the label-free capture of CTCs from blood samples, with high CTC recovery, purity and compatibility with downstream genomic assays on CTCs and plasma3,4. Our combined CTC and ctDNA EGFR assay was applied to blood samples from NSCLC patients. Method ctEGFR kit (EntroGen) was selected and validated for the detection of EGFR major mutations in a single PCR reaction, for both ctDNA and CTCs. Several blood collection tubes (BCT: EDTA, CellSave, LBGard and Streck) were tested using spiked cells, considering CTC recovery, DNA yield, and EGFR profiling. 20 blood samples were studied from 15 NSCLC patients. Plasma was extracted for ctDNA assay. CTCs were isolated from the plasma-depleted-blood using the VTX-1, immunostained and enumerated5. EGFR mutations were then detected in CTC+ctDNA, and compared to the tissue results. Results The VTX-1 provided a similar CTC recovery from plasma-depleted-blood and whole blood, enabling CTC+ctDNA EGFR profiling from the same tube of blood. Among the BCTs tested, LBGard obtained the best CTC capture and EGFR mutation detection performance. 10/15 patients showed the same mutations between tissue and CTC+ctDNA. For one patient with two blood draws without mutation in tissue, no mutation was detected in the first draw, while a T790M mutation was identified 6 months later. For another patient, an Exon19 deletion was detected in the ctDNA+CTC but not in the tissue, and a repeat draw confirmed the result. 4/15 patients had mutations in tissue that were missed in CTC+ctDNA. Conclusion Performing EGFR mutation analysis on the combination of ctDNA and VTX-1-collected CTCs may offer a