Abstract
PURPOSE: Changes in ctDNA levels during systemic treatment may predict treatment efficacy in patients with metastatic pancreatic ductal adenocarcinoma (PDAC), but quantitative response criteria are not yet established. This study evaluates our recently proposed ctDNA-RECIST. EXPERIMENTAL DESIGN: Blood samples were collected before treatment, before the second treatment cycle, and at the time of the first CT evaluation from 220 patients with metastatic PDAC receiving first-line palliative chemotherapy. Plasma ctDNA levels were measured using Droplet Digital PCR with HOXA9 methylation assays. ctDNA response was determined according to ctDNA-RECIST and correlated with overall survival (OS). RESULTS: ctDNA was positive before treatment in 71% of the patients and was related to OS [HR = 1.61; 95% confidence interval (CI), 1.19-2.19; P = 0.002]. Among ctDNA-positive patients, ctDNA maximal response (MR; n = 41) and ctDNA disease control (DC; n = 107) before the second treatment cycle had longer OS compared with ctDNA progressive disease (PD; n = 5; median OS: MR 11.9 months, DC 7.2 months, PD 3.6 months; P = 0.002). In Cox regression, ctDNA DC (HR = 1.55; 95% CI, 1.07-2.26; P = 0.021) and ctDNA PD (HR = 4.50; 95% CI, 1.74-11.6; P = 0.002) showed shorter OS compared with ctDNA MR. The same applied to ctDNA response at the time of the first CT evaluation assessed from the second treatment cycle (P < 0.001) and from treatment start (P < 0.001). CONCLUSIONS: ctDNA-RECIST applied to liquid biopsies holds potential for early evaluation of treatment benefit in patients with metastatic PDAC, offering a novel, minimally invasive method to guide early clinical decision-making. Future studies should validate ctDNA-RECIST prospectively, preferably in randomized controlled trials.