Background: HA is a major component of the tumor microenvironment (TME) in PDA. PEGPH20 degrades tumor HA, remodeling the TME. In PDA models, PEGPH20 has shown antitumor activity and increased TME delivery of anticancer agents to improve efficacy. A randomized phase 2 study showed promising results for PEGPH20+AG (PAG) in mPDA and identified HA accumulation as a biomarker. We present results from a phase 3 study (NCT02715804) of PAG for pts with HA-high mPDA. Methods: Pts ≥18 years with untreated HA-high mPDA were randomized (stratified by geographic region) 2:1 to PAG or placebo+AG (AG). HA status was prospectively determined with VENTANA HA RxDx Assay, with HA-high defined as ≥50% staining of a tumor sample. Treatment was administered IV in 4-wk cycles (3 wks on, 1 wk off) until progression or intolerable adverse events (AEs): PEGPH20 3.0 µg/kg twice wkly for Cycle 1 and once wkly (QW) thereafter, A 125 mg/m² QW and G 1000 mg/m² QW. Prophylactic enoxaparin 1 mg/kg was given daily for thromboembolism (TE) risk. The primary endpoint was overall survival (OS); secondary endpoints included progression-free survival (PFS), objective response rate (ORR) and safety. Response was independently assessed per RECIST v1.1. The estimated sample size was ~500 pts to detect a hazard ratio (HR) for OS of 0.67 (93% power, 2-sided α = 0.05) after 330 deaths. Results: As of 20 May 2019, 494 pts were randomized with 492 (327 for PAG and 165 for AG) included in ITT analyses (2 pts excluded due to site violations). Baseline characteristics were balanced for PAG vs AG. After 330 deaths, median OS for PAG vs AG was 11.2 vs 11.5 mo (HR 1.00, 95% CI 0.80–1.27; P = 0.97); median PFS was 7.1 vs 7.1 mo (HR 0.97, 95% CI 0.75–1.26); confirmed ORR was 34% vs 27%. Grade (G) 3+ AEs (PAG vs AG) included neutropenia (44% vs 47%), thrombocytopenia (21% vs 16%) and fatigue (16% vs 10%); G3+ rates were 6% vs 7% for TE events, 5% vs 2% for bleeding events and 13% vs 5% for musculoskeletal events. Conclusions: PAG did not improve clinical outcomes vs AG. The PAG safety profile was consistent with that of previous studies. Clinical trial information: NCT02715804