Kundranda MN, et al. - In this laboratory blinded, prospective single-institution study, researchers compared prospectively computed copy number instability (CNI) scores of cell-free tumor DNA (cfDNA) to radiology and Ca 19-9 for predicting therapeutic response in patients (pts) with PDAC. They analyzed 119 plasma samples from 33 pts. CNI Score (CNIs) of 31 was defined as ref. range (97.5 % - control group; N = 135), pts below this threshold were censored. Standard radiological imaging offered a classification of 33 pts as: 14 PR/CR, 10 SD, 9 progression of disease (PD). A total of 27/33 pts (81%) were evaluable by CNIs which ranged from decrease of 2017 - increase of 645. For predicting PD and for SD/PR/CR, a sensitivity of 86% and 95%, respectively, was displayed by the C3 CNI classifier. Findings revealed potentially superior reliability of CNI quantification as a blood-based marker for early assessment of efficacy to systemic therapy in PDAC. It could be an alternative monitoring aid for patients not expressing CA19-9.