Background: Rigosertib (ON 01910.Na), a dual non-ATP inhibitor of polo-like kinase 1 (Plk1) and phosphoinositide 3-kinase (PI3K) pathways, was assessed in patients with treatment-naïve metastatic pancreatic adenocarcinoma. Methods: Patients with metastatic adenocarcinoma of the pancreas were randomized in a 2:1 fashion to gemcitabine 1000 mg/m² weekly for 3 weeks of a 4-week cycle plus rigosertib 1800mg/m² via 2-hr CIV infusions given twice weekly for 3 weeks of a 4-week cycle versus gemcitabine 1000mg/m² weekly for 3 weeks in a 4-week cycle. Results: A total of 160 patients were enrolled globally and randomly assigned to rigosertib plus gemcitabine (106 patients) or gemcitabine (54). The most common grade 3 or higher adverse events were neutropenia (8% in the rigosertib plus gemcitabine group vs. 6% in the gemcitabine group), hyponatremia (17% vs. 4%), and anemia (8% vs. 4%). The primary outcome of the study, median OS, was 6.1 months in the gemcitabine plus rigosertib arm versus 6.4 months with gemcitabine alone (hazard ratio (HR), 1.24; 95% confidence interval [CI], 0.85-1.81). The median PFS was 3.4 months for both groups (HR, 0.96; 95% CI, 0.68-1.36). The overall best response between arms were partial response rates of 19% versus 13% and stable disease in 50% versus 56% in the gemcitabine plus rigosertib versus gemcitabine alone, respectively. Of 64 tumor samples sent for molecular analysis, 47 were adequate for multiplex genetic testing and 41 were positive for mutations. The majority of cases had KRAS gene mutations (40/47, 85%), which included c.35G>T, p.G12V (12 cases), c.35G>A, p.G12D (21 cases), c.34G>C, p.G12R (4 cases), c.34G>T, p.G12C (1 case) and c.183C>A, p.Q61H (2 cases). Other mutations detected included TP53 (13 cases) and PIK3CA(1 case). No correlation between mutational status and efficacy was detected. Conclusions: The combination of rigosertib plus gemcitabine failed to demonstrate an improvement in survival or response compared to gemcitabine alone in metastatic pancreatic adenocarcinoma. Clinical trial information: NCT01360853