Background: Subgroup analyses of the NAPOLI-1 study identified that among patients who were IRI naïve prior to entering the clinical trial, a survival benefit was observed between the study arm and control arm (overall survival (OS): 6.7 months vs 4.2 months). This treatment benefit was not observed among those previously exposed to IRI (OS: 4.6 months in study arm vs 4.8 months in control arm). This study sought to understand the impact of prior exposure to IRI on clinical outcomes among patients treated with liposomal irinotecan in the real-world setting. Methods: This retrospective observational study utilized the Flatiron Health EHR database. Data were analyzed for adult patients with mPDAC treated with liposomal irinotecan -based regimens between January 2016 and October 2020. Patient characteristics, OS and progression-free survival (PFS) were assessed. Prior IRI was defined as IRI given in a prior regimen in the metastatic setting. Cox proportional hazard (PH) methods were used to calculate hazard ratios (HRs). HRs were adjusted to account for demographics and relevant clinical covariates. Patients without prior exposure to IRI were used as the reference population for the Cox PH model (an HR < 1 represents worse survival for unexposed patients relative to the exposed). Results: 675 patients with mPDAC treated with a liposomal irinotecan-based regimen were included. Median age at treatment initiation was 69 (IQR: 62 – 75) years and among patients with available ECOG performance status (PS), 77.4% had a PS of 0-1. 181 (27%) patients were previously exposed to IRI in the metastatic setting (Table). The unadjusted OS HR was 1.3 (95% CI: 1.1 – 1.6, p < 0.001) and the unadjusted PFS HR was 1.4 (95%CI: 1.2 – 1.7, p < 0.001). After adjustment for baseline characteristics the adjusted OS HR was 1.0 (95% CI: 0.8 – 1.3, p = 0.8836) and the adjusted PFS HR was 1.1 (95%: 0.8 – 1.4, p = 0.5626). Conclusions: The results of this study suggest prior exposure to IRI is not a predictor of worse clinical outcomes for patients treated with liposomal irinotecan-based treatment when accounting for key clinical characteristics in a multivariable model. The results from this real-world study can be used to support treatment sequencing decisions for patients with mPDAC following first line therapy. This is the largest real-world evidence study to date of patients with mPDAC treated with liposomal irinotecan.