1640P Response monitoring with ctDNA in metastatic pancreatic cancer

e16284 Background: Various studies about clinical usefulness of serial monitoring with liquid biopsy are being conducted actively in many types of cancer. However, there is not much in pancreatic cancer. We explored whether serial ctDNA monitoring in metastatic pancreatic cancer (MPC) can be beneficial for evaluating treatment response and predicting prognosis. Methods: A total of 51 MPC patients were prospectively enrolled. Blood samples were collected at every response evaluation until progression of disease (PD) or 5 th evaluation. Quantitative ctDNA were measured by droplet digital polymerase chain reaction using KRAS G12/G13 screening multiplex Kit (Bio-Rad) and reported as variant allele fraction (VAF). Percent change of ctDNA VAF (DctDNA(%) = (current VAF - previous VAF)/previous VAF*100) were correlated to radiographic responses by RECIST 1.1. Furthermore, Progression free survival (PFS) and overall survival (OS) were analyzed by DctDNA. Results: Among the 51 enrolled patients, baseline ctDNA were detected in 35 patients. During a median follow-up of 9.4 months, PD by radiographic response was observed in 24 patients. As expected, PD group showed higher DctDNA compared with non-PD group (p<0.001). DctDNA for PD yielded Area Under Curve of 0.914 (p<0.001) with 83.3% sensitivity at 90% specificity. Patients who showed early ctDNA clearance (undetectable level at first response evaluation) had longer PFS (8.1 m vs 4.7 m; HR 0.46; 95% CI 0.20 to 1.03; p=0.059) and OS (not reached vs 8.0 m; HR 0.20; 95% CI 0.06 to 0.74; p=0.009) than those who did not. In multivariable analysis, early ctDNA clearance was still associated with significantly longer PFS (HR 0.27; 95% CI 0.08 to 0.92, p=0.036) and OS (HR 0.08; 95% CI 0.02 to 0.54, p=0.007). Conclusions: Serial monitoring with ctDNA in MPC has considerable clinical potential in monitoring treatment response and predicting prognosis.