Background: Interleukin-6 (IL-6) and YKL-40 (CHI3L1) are produced by pancreatic cancer (PC) cells and macrophages and activate inflammation. The aim of this prospective-retrospective biomarker study was to determine the prognostic value of serum IL-6 and YKL-40 and systemic inflammatory response in patients with PC receiving palliative chemotherapy. Methods: 625 patients with PC (M/F: 283/342; age <70 vs. ≥70: 395/230; ECOG PS of 0/1/2/3: 214/315/92/4; stage 3 vs. 4: 129/496; treated with gemcitabine n=437, FOLFIRINOX n=117, gemcitabine and nab-Paclitaxel n=54 or other n=17) were included in the BIOPAC biomarker study from 5 hospitals in Denmark. Pretreatment serum values of IL-6 (R&D Systems), YKL-40 (Quidel), and CA 19-9 (Siemens) were determined. Patients were grouped as low vs. high, dichotomized using cut-off for IL-6 > 4.92 pg/ml, for CA19-9 > 2183 U/ml and for YKL-40 > 95% age-corrected percentile. The main outcome was overall survival (OS) and hazard ratios (HRs) and corresponding 95% confidence intervals (CIs) were computed using Cox proportional hazards regression. Results: 598 (95.7%) patients died during follow-up. In univariate analysis elevated IL-6 (HR 1.93, 95% CI 1.63-2.28) and elevated YKL-40 (HR 1.74, 95% CI 1.47-2.05) were associated with short OS. Similar results were found if IL-6 and YKL-40 were included as continuous log2-transformed variables. Multivariable analysis showed that elevated IL-6 (HR 1.61, 95% CI 1.33-1.94), elevated YKL-40 (HR 1.36, 95% CI 1.13-1.64), elevated CA19-9 (HR 1.30, 95% CI 1.09-1.56), higher PS (1 vs. 0; HR 1.46, 95% CI 1.21-1.77 and PS 2 vs. 0; HR 2.73, 95% CI 2.08-3.58) and stage 4 vs. 3 (HR 1.79, 95% CI 1.44-2.24) were independently associated with a poor OS. In a subgroup of 386 patients with available laboratory data, higher C-reactive protein (HR 1.20, 95% CI 1.13-1.26), white blood cells (HR 1.41, 1.17-1.71) and absolute neutrophils count (HR 1.35, 95% CI 1.15-1.59) log2-transformed and adjusted for age, sex, PS, CA 19-9 and stage were associated with short OS. Conclusions: Serum IL-6, YKL-40 and CA19-9 along with CRP, WBC and ANC are independent prognostic biomarkers in patients with unresectable PC.