Background: The incidence of PDAC is on the rise and it is predicted to be the 2nd leading cause of cancer related mortality in the next decade. Most patients present with advanced disease at diagnoses with limited systemic treatment options. Fluoropyrimidines are active in PDAC. Lonsurf (L) is an orally administered combination of a thymidine-based nucleic acid analogue, trifluridine, and a thymidine phosphorylase inhibitor, tipiracil hydrochloride. Preclinical data demonstrate Lonsurf may have activity in 5-FU resistant malignancies. This phase I study combines Gem, nab-P, and L. Methods: Gem and nab-P are dosed on days 1 and 15 IV on a 28 day cycle. L (20-30mg/m2) is dosed twice daily on days 2-6 and 16-20 (table 1). Dose escalation is by 3+3 design. Key eligibility include pts with untreated locally advanced or metastatic PDAC, ECOG 0-1, and adequate hepatic and bone marrow function. Results: 14 pts (median age 62 yrs [range 43-74]) have been enrolled. Dose was initiated at DL1. The first 3 pts were treated without DLT. DL2 exceeded the MTD with 1 patient experiencing grade 3 infection (cholangitis). Dose expansion to 7 patients was completed at DL 1 with no further DLTs. The RP2D is Gem 800mg/m², Nab-P 100mg/m², and L 25mg/m². Of the 10 patients with evaluable disease, 2 (20%) had PR and 7 (70%) had SD. Pts were on study a median of 14 months (range 4 -31+). Most common grade 3/4 AEs include fatigue (46%,) neutropenia (38%), anemia (31%) anorexia (15%), nausea (15%), vomiting (15%), abdominal pain (15%), hyperglycemia (15%). No grade 5 events occurred. Conclusions: The RP2D is Gem 800mg/m², Nab-P 100mg/m², and L 25mg/m². This combination was well tolerated with expected toxicities of myelosuppression with prolonged responses seen. Clinical trial information: NCT04046887.