Background: Poor outcome in pancreatic cancer (PDA) has been associated with tumor stroma limiting access of chemotherapy drugs. PEGPH20 (PEG), PEGylated recombinant human hyaluronidase, which depletes hyaluronan (HA) in tumors, has demonstrated anti-tumor activity in preclinical PDA models. In a KPC model of PDA, PEG + gemcitabine (Gem) significantly prolonged survival compared to Gem alone. In Phase 1 PEG monotherapy studies, the MTD was 3µg/kg. The most common adverse events (AEs) were musculoskeletal events. Methods: This was a phase 1b study to determine the recommended phase 2 dose of PEG + Gem in patients (pts) with previously untreated Stage IV pancreatic cancer. PEG was given at 1, 1.6, or 3µg/kg IV twice weekly Wks 1–4 and weekly Wks 5–7, followed by 1 wk rest. Gem was given at 1000mg/m²IV once weekly for Wks 1–7, then 1 wk rest. Thereafter, PEG + Gem were given once weekly for 3 wks in 4-wk cycles. Dexamethasone was given pre and post PEG doses. Due to evolving SOC, the study was discontinued before initiation of the phase 2 randomization. Results: Twenty-eight pts were enrolled in the study. The majority of the patients (89%) had metastatic sites in the liver. Four, 4 and 20 pts received PEG at 1, 1.6 and 3µg/kg, respectively. The most common AEs related to PEG were muscle spasm (54%), myalgia (39%), arthralgia (29%), peripheral edema (29%), fatigue (25%), and extremity pain (18%). Median progression free survival (PFS) and overall survival (OS) were assessed and were 154 and 200 days, respectively. In an exploratory analysis, tumor biopsies from 17 pts were evaluated for HA levels (HA^high or HA^low). 6 pts were determined to have HA^high tumors and 11 pts had HA^low tumors. The median PFS and OS for HA^high pts were 219 days (95% CI: 159-276) and 395 days (95% CI: 210-578). For HA^lowpts median PFS and OS were 108 (95% CI: 14-163) and 174 days (95% CI: 34-293). Conclusions: PEG + Gem is generally well tolerated in advanced pancreatic cancer and shows promising clinical activity, especially in pts with HA^high tumors. ClinicalTrials.gov Identifier: NCT01453153.