Background: Pancreatic cancer (PC) is characterized by a highly immunosuppressive microenvironment, and immune checkpoint inhibitors as monotherapy have been ineffective to date. TGFβ is commonly viewed as a powerful immunosuppressive cytokine, and inhibition of its signaling reverses this suppression and activates adaptive immune responses. A combination of TGFβ and PD-L1 inhibition may act synergistically to induce immune restoration and to improve antitumor responses. This Phase 1b study (NCT02734160) evaluated the combination of galunisertib plus durvalumab in recurrent or refractory metastatic PC. Methods: Eligible patients (pts) were ≥18 years old, had ECOG status ≤1, and had not received treatment with anti-PD-1, anti-PD-L1, or TGFβ R1 kinase inhibitors. The primary objective was to assess the safety and the recommended dose of galunisertib given 14 days on/14 days off in combination with durvalumab 1500 mg every 4 weeks. Four dose levels of galunisertib were tested in the dose escalation portion of the study: 50 mg QD, 50 mg BID, 80 mg BID and 150 mg BID, followed by the cohort expansion portion of the study at the recommended Phase 2 dose (RP2D). Secondary objectives included preliminary assessment of activity by response rate, (RECIST v1.1), median PFS (mPFS), and OS (mOS). Results: 42 pts (25F/17M) were treated in the study (median age 56.5 y; 71.4% had received ≥2 prior systemic regimens). There was no dose limiting toxicity and galunisertib 150 mg BID was chosen as the RP2D. In the 32 pts treated at this dose, Grade ≥3 related AEs included AST and GGT elevations (2 pts each), and ALT and alkaline phosphatase elevations, and neutropenia (1 pt each). One partial response and 7/32 stable diseases were observed (disease control rate 25%); mPFS was 1.9 months (95% CI: 1.5, 2.2) and mOS was NR (95% CI: 3.6, NR). Biomarker data will be presented at the meeting. Conclusions: The combination of galunisertib plus durvalumab had an acceptable tolerability and safety profile. The activity of this combination in second and third line PC patients warrants further consideration. Clinical trial information: NCT02734160