Liquid biopsies of plasma exosomal nucleic acids, plasma cell-free DNA, and survival of patients with advanced cancers.

Abstract

11551 Background: Blood-based liquid biopsies offer easy accessible genomic material for molecular diagnostics in cancer. Commonly used cell-free DNA (cfDNA) originates from dying cells. In contrast exosomal nucleic acid (exoNA) originates from living cells, which can better reflect underlying cancer biology. Methods: We isolated exoNA (EXO52) and cfDNA (QIAamp Circulating Nucleic Acid kit) from plasma of patients with progressing advanced cancers and tested for BRAFV600, KRASG12/G13, and EGFRexon19del/L858R mutations using next-generation sequencing (EXO1000), droplet digital PCR (ddPCR, QX200) and BEAMing digital PCR. The results were compared to clinical testing of archival tumor tissue and correlated with survival. Results: Of the 43 patients (colorectal cancer, 20; melanoma, 8; non-small cell lung cancer, 6; ovarian cancer, 2; papillary thyroid cancer, 2; other cancers, 5) 41 had a mutation in the tumor tissue (20 [47%] BRAF mutation, 17 [40%] KRAS mutation and 4 [9%] EGFR mutation). Mutation testing of plasma exoNA from all 43 patients detected 39 (95%) of 41 mutations present in tumor tissue with 100% specificity. Mutation testing of plasma cfDNA from 39 patients using ddPCR detected 33 (89%) of 37 mutations present in tumor and testing of plasma cfDNA from 37 patients using BEAMing detected 34 (97%) of 35 mutations present in tumor tissue; however, both cfDNA methods reported an additional KRAS mutation not present in tumor tissue. Patients with high mutation allele frequency (MAF, > median) had shorter median survival compared to patients with low MAF ( < median) when using exoNA (5.9 vs. 11.8 months, P= 0.006), but not cfDNA ddPCR (6.0 vs. 7.4 months, P= 0.06) or cfDNA BEAMing (6.5 vs. 7.4 month, P= 0.07). High MAF in exoNA was an independent prognostic factor for survival in multicovariate analysis (HR 0.13, P= 0.017). Conclusions: Mutation testing of plasma exoNA for common BRAF, KRAS, and EGFR mutations has high sensitivity compared to clinical testing of archival tumor tissue and better specificity than PCR testing of plasma cfDNA. High MAF in exoNA is the independent prognostic factor for shorter survival.