LAUSR

e15763 Background: This study was to investigate the feasibility and the prognostic value of circulating tumor DNA (ctDNA) in metastatic pancreatic cancer (MPC). Methods: From 2015 to 2018 in our center, 40 MPC patients treated with nab-paclitaxel based first-line chemotherapy were prospectively collected both tumor tissue and blood samples, in which the genomic profiling of 425 genes was identified by next-generation sequencing. High mutation allelic frequency (MAF) was defined > 30% and > 5% in tumor tissue and blood, respectively. Kappa statistics were used to compare mutant (mt) genes in tissue and ctDNA. Progression-free and overall survival (PFS, OS) were assessed with Kaplan-Meier and Cox methods. Results: Among 40 MPC patients, tumor tissue and blood samples were available in 34 and 38 patients for somatic and germline alternation test, respectively. The most commonly mutant gene were KRAS (31/34 in tissue with a median MAF of 29.4%, 29/38 in ctDNA with a mMAF of 8.2%), and TP53 (28/34 in tissue with a mMAF of 31.1%, 25/38 in ctDNA with a mMAF of 7.4%). Moderate agreement was seen between ctDNA and tumor tissue (mt KRAS: κ = 0.54, P = 0.001; mt TP53: κ = 0.74, P < 0.001). Mutation in CDNK2A and SMAD4 genes were detected in 8 and 6 patients in tissue and ctDNA, respectively. Germline alternation was found in 7 genes in 9 patients (9/40). High MAF of mt KRAS (r = 0.51, P = 0.005) or mt TP53 (r = 0.50, P = 0.005) in ctDNA was correlated with high CA199 levels (> 5000 u/ml) at baseline. MT KRAS in tissue with high MAF was associated with poor OS (high 7.5m vs low 10.1m, P = 0.001) in univariate and multivariate analyses (HR 3.87, 95%CI 1.47 to 10.19). Univariate analyses showed mt KRAS and mt TP53 in ctDNA with high MAF were associated with poor PFS ( KRAS and TP53: high 3.4m and 3.0m vs low 6.1m and 5.7m, P = 0.001 and P = 0.004, respectively) and OS ( KRAS and TP53: high 5.3m and 5.3m vs low 12.6m and 10.1m, P < 0.001, respectively). The presence of ctDNA in any above four mt driver gene with high MAF was associated with poor PFS (HR 3.79, 95%CI 1.71 to 8.42) and OS (HR 7.21, 95%CI 2.69 to 19.34) in multivariate COX model, when adjusted by age, sex, tumor differentiation, and baseline CA199 level. Conclusions: The presence of mt KRAS and mt TP53 with high MAF in ctDNA was associated with worse PFS and OS in MPC patients. Peripheral ctDNA testing demonstrated an alternative promising prognostic biomarker for MPC patients before treatment.