A Multicenter Study to Assess EGFR Mutational Status in Plasma: Focus on an Optimized Workflow for Liquid Biopsy in a Clinical Setting

Abstract

A multicenter study was performed to determine an optimal workflow for liquid biopsy in a clinical setting. In total, 549 plasma samples from 234 non-small cell lung cancer (NSCLC) patients were collected. Epidermal Growth Factor Receptor (<i>EGFR)</i> circulating cell-free tumor DNA (ctDNA) mutational analysis was performed using digital droplet PCR (ddPCR). The influence of (pre-) analytical variables on ctDNA analysis was investigated. Sensitivity of ctDNA analysis was influenced by an interplay between increased plasma volume (<i>p</i> < 0.001) and short transit time (<i>p</i> = 0.018). Multistep, high-speed centrifugation both increased plasma generation (<i>p</i> < 0.001) and reduced genomic DNA (gDNA) contamination. Longer transit time increased the risk of hemolysis (<i>p</i> < 0.001) and low temperatures were shown to have a negative effect. Metastatic sites were found to be strongly associated with ctDNA detection (<i>p</i> < 0.001), as well as allele frequency (<i>p</i> = 0.034). Activating mutations were detected in a higher concentration and allele frequency compared to the T790M mutation (<i>p</i> = 0.003, and <i>p</i> = 0.002, respectively). Optimization of (pre-) analytical variables is key to successful ctDNA analysis. Sufficient plasma volumes without hemolysis or gDNA contamination can be achieved by using multistep, high-speed centrifugation, coupled with short transit time and temperature regulation. Metastatic site location influenced ctDNA detection. Finally, ctDNA levels might have further value in detecting resistance mechanisms.