Background: GCSF is used for primary/secondary prophylaxis of chemotherapy(chemo)-associated neutropenia in patients (pts) with mPDAC. GCSF may also increase the populations of healthy, naïve immune cells in an otherwise immunologically dysregulated and cold environment, potentially augmenting therapy outcome with immunomodulatory (IO) agents. Here, we describe the impact of GCSF administration on OS, PFS, and time on treatment (TOT) in the setting of mPDAC for (1) a trial in which pts were administered chemo-IO combinations and (2) a synthetic control arm using retrospective real-world data from pts who received standard-of-care (SOC) chemo (PASCAL). Methods: PRINCE is a ph1b/2 study evaluating gemcitabine (gem) and nab-paclitaxel (NP) ± sotigalimab (sotiga; CD40 agonist) ± nivolumab (nivo; anti-PD1) for pts with mPDAC (NCT0324250), where prophylactic GCSF use was prohibited. PASCAL pts received SOC gem/NP and primary/secondary GCSF use was allowed. In this retrospective analysis, GCSF use was defined as receiving at least 1 dose of GCSF anytime during treatment. OS, PFS, and TOT and associated HRs and CIs were calculated using Kaplan-Meier and Cox methods. PFS data not available for PASCAL. Results: 32/123 (26%) and 16/68 (24%) pts received GCSF in PRINCE and PASCAL, with 84% and 88% of pts receiving at least 1 dose within the first 3 cycles, respectively. In PRINCE, GCSF use was associated with significant improvements in OS (HR [95% CI]: 0.62 [0.40-0.97]), PFS (0.71 [0.47-1.08]), and TOT (0.67 [0.45-1.01]). These improvements were most notable in the sotiga-containing arms (table). In the absence of IO treatment, however, no statistical significance was observed in PASCAL (HR [95% CI]: OS = 0.81 [0.44-1.51]; TOT = 0.90 [0.51-1.58]). Additional work is ongoing to understand the association of GCSF usage with known prognostic factors. Conclusions: These analyses suggest that GCSF use may enhance the clinical benefits of chemo-IO in mPDAC. These potential benefits of GCSF usage warrant further evaluation in other chemo-IO trials as well as prospective evaluation in pre-clinical and clinical settings. Clinical trial information: NCT03214250.