Circulating tumor DNA (ctDNA) has emerged as a specific and sensitive blood-based biomarker for detection of several mutations in non–small-cell lung cancer (NSCLC). Other clinical applications include serial monitoring of biomarker status or the development of resistance mutations.
Forty patients with advanced NSCLC who either had a new diagnosis (group 1) or had developed acquired resistance to an EGFR kinase inhibitor (group 2) were analyzed with the highly sensitive Biocept, Inc Target-SelectorTM Real-Time PCR based plasma assays genotyping for the detection of EGFR mutations L858R, Del19 and T790M. In addition, group 1 patients were analyzed for KRAS and BRAF mutations with the same methodology; ROS1 and ALK were analyzed by FISH on captured circulating tumor cells (CTCs) with the same platform before and after TKI treatment. Tumor tissue was analyzed with Real-Time PCR and FISH based assays.
Results showed up to 90% concordance rate of EGFR, KRAS and ALK alterations for between the tissue and blood samples. The T790M mutation appeared in 50% of plasma samples analyzed in patients with clinical progression after TKI inhibitors. Group 1 paired analysis of mutations status monitoring (P= 0.016) showed that the pattern of mutant ctDNA and CTCs changed in response to systemic therapy in 83% of the cases (partial response or disease progression; R2 = 0.808). ctDNA analysis of multiple mutations on group 1 showed: 1) 40% of patients had at least one or more new mutation different than the one detected in tissue biopsy; 2) 28% of EGFR tissue positive patients also had a KRAS mutation: 3) 75% of KRAS positive patients had a BRAF mutation. This technique may be sensitive enough to detect mutations missed by standard tissue genotyping probably due to tissue heterogeneity.
Target-SelectorTM ctDNA and CTC assays appear capable of rapidly detecting EGFR and KRAS mutations as well as ALK rearrangements. It is highly concordant with mutations present in tumor tissue. It would seem to be a viable alternative to identify secondary EGFR mutations such as T790M.
Clinical trial identification
Legal entity responsible for the study
National Cancer Institute. Mexico
L. Barrera, J.R. Borbolla: AstraZeneca full-time employee L. Arnold, J. Poole, V. Alexiadis, B. Gustafson, V. Singh: Biocept, Inc. full-time employee. All other authors have declared no conflicts of interest.