Background: Whilethe systemic inflammatory response assessed by SIRI has been recognized as a prognostic factor in advanced pancreatic cancer, understanding its association with patients' nutritional status may provide deeper insights into disease biology and outcomes. Methods: This is an observational, non-interventional and multicenter study (15 Spanish hospitals) promoted by SEOM, including retrospective and prospectively patients with metastatic pancreatic cancer in routine clinical practice. Clinical and nutritional data was recorded, and SIRI was calculated using the formula: (neutrophils x monocytes) / lymphocytes. We considered SIRI score as low (SIRI-L) or high (SIRI-H) using a cutoff of <2.3 or ≥2.3, respectively based in our previous findings. PANDORA-SEOM tool was used for electronic data collection. The main outcome is to correlate SIRI with the nutritional status. Other aims were to correlate the overall survival (OS) and progression-free survival (PFS) with SIRI and weight loss in the 3 months prior to diagnosis using the Kaplan-Meier method and multivariate Cox regression model. Data from the pilot study is presented in this abstract, and more data is expected to be available prior to the Congress. Results: We included 144 patients retrospectively: 65% men, with median age of 66 years (range 45-81). The most common 1^st line chemotherapy regimen were gemcitabine + nab/paclitaxel (63.2%), mFOLFIRINOX (20.1%) and FOLFOX (11.8). Prior to diagnosis, 54.2% of patients had weight loss >5 Kilograms (Kg) and 22.9% lost >10 Kg. SIRI-H was significantly associated with weight loss >5Kg compared to SIRI-L, 35.7 vs 24% respectively (p=0.028). Patients with a pretreatment SIRI-H showed shorter OS compared to SIRI-L (median OS 5 vs 12 months, Hazard Ratio (HR) 3.047, 95% Confidence Interval (CI) 2.069-4.488, p<0.001), as well as shorter PFS (median PFS 5 vs 10 months, HR 2.364, 95% CI 1.650-3.387, p<0.001). In the patient subgroup that experienced >5Kg weight loss, SIRI-H was associated with worse OS (median OS 4 vs 12 months). We didn’t find an association between CA19.9 level and SIRI or weight loss. Multivariate analysis identified SIRI as an independent prognostic factor for OS (HR 2.962, 95% CI 1.911-4.591, P<0.001). Conclusions: Our findings underscore the importance of SIRI as a significant predictor of nutritional status and disease aggressiveness in patients with metastatic pancreatic cancer. Prospective data will help us to validate these findings.