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4139 Background: Nearly all stage IV pancreatic adenocarcinoma (PAC) patients progress after first-line treatment, and second-line options are limited. SGT-53 is an investigational product for tumor-targeted TP53 gene therapy that has completed phase Ia/Ib trials [Senser et al (2013), Mol Ther 21:1096; Pirollo et al (2016) Mol Ther 24:1697]. Methods: Here we provide an interim analysis of a Phase II trial (SGT53-02-1; NCT02340117) combining SGT-53 with gemcitabine/nab-paclitaxel (GEM/ABX). Eligible were first-line patients or those who had progressed after FOLFIRINOX (FFX) and/or gemcitabine-based therapy (second-line). In a 7-week treatment cycle, SGT-53 (3.6 mg DNA) was given once or twice weekly with GEM/ABX (1000 mg/m2/wk and 125 mg/m2/wk, respectively, for 3 of 4 weeks). Progression-free survival (PFS) and objective response rate (ORR) are primary endpoints.Overall survival (OS) and PFS are estimated by Kaplan-Meier analysis. Results: Of all evaluable patients (n=20), best response in 7 patients was determined to be partial response (PR) and 13 had stable disease (SD); none had progressive disease. In the second-line patients (n=11) there were 5 PR and 6 SD after 9 had failed FFX treatment, 3 had failed gemcitabine-based treatment and 1 had failed both. For patients with elevated CA19-9, SGT-53 + GEM/ABX resulted in marked reductions in the tumor marker. Published data for patients with PAC after therapy failure [Mita et al (2019) J Clin Med 8: 761; Portal et al (2015) Br J Cancer 113:989; Wang-Gillam et al (2016) Lancet 387:545] are shown for comparison. Notably, mPFS in our second-line patients was 7.4 months versus 3.1 months for the approved second-line therapy [Wang-Gillam et al (2016)]. This improvement in PFS exceeds the benchmark proposed to predict a clinically meaningful Phase III trial [Rahib et al (2016) Lancet Oncol 2:1209]. Conclusions: Our data suggest a clinically meaningful benefit of adding SGT-53 to GEM/ABX particularly for second-line PAC patients, most of whom had failed prior FFX treatment. Clinical trial information: NCT02340117. [Table: see text]