ObjectiveTo determine the prognostic significance of change of systemic immune inflammation index (SII) before and after neoadjuvant chemotherapy (NCT) in advanced pancreatic cancer.MethodsThe patients with advanced pancreatic cancer who received the NCT before pancreatectomy and met the inclusion and exclusion criteria of this study from January 2013 to December 2016 in the Panjin Liao-Oil Gem Flower Hospital were retrospectively collected. The patients were designed into an increased SII group (SII before NCT was lower than after NCT) and decreased SII group (SII before NCT was higher than after NCT) according to the change of SII before and after NCT. The laboratory data before and after NCT were collected to calculate the SII and to analyze the relationship between the change of SII before and after NCT and the clinical outcomes. The clinicopathologic characteristics and postoperative 3-year survival rate of the two groups were compared. The Cox regression was used to evaluate the influencing factors of postoperative survival of advanced pancreatic cancer.ResultsAll of 103 patients were included, 42 of whom in the increased SII group and 61 in the decreased SII group. The proportions of the intraoperative tumor size >3 cm, CA19-9>37 U/mL after NCT, and postoperative complications in the increased SII group were significantly higher than those in the decreased SII group (P<0.05). All 103 patients were followed up from 9 to 81 months with median 13 months, the 3-year cumulative survival rate of patients in the increased SII group was significantly lower than that of patients in the decreased SII group (19.0% versus 42.6%, P=0.012). The results of the multivariate analysis showed that the CA19-9>37 U/mL after NCT [HR=2.084, 95%CI (1.140, 3.809), P=0.017], postoperative complications [HR=1.657, 95%CI (1.009, 2.722), P=0.046], the absent of postoperative adjuvant chemotherapy [HR=1.795, 95%CI (1.085, 2.970), P=0.023], and the elevated SII after NCT [HR=1.849, 95%CI (1.111, 3.075), P=0.018] were the independent risk factors affecting postoperative 3-year survival rate of patients with advanced pancreatic cancer.ConclusionsThe change value of SII before and after NCT is an independent risk factor for the prognosis of patient with advanced pancreatic cancer, the elevated SII after NCT is a poor prognosis index in patient with advanced pancreatic cancer. However, the evaluations of larger controlled trials are necessary at multiple institutions before introduction of SII as a prognostic indicator in clinical practice.