Pretreatment systemic immune-inflammation index predicts survival for non-metastatic nasopharyngeal carcinoma:two independent institutional studies

Objective:This study aimed to evaluate the prognostic value of the pretreatment systemic immune-inflammation index(SII)in non-metastatic nasopharyngeal carcinoma(NPC).Methods:We retrospectively analyzed the data of 839 patients with non-metastatic NPC recruited from two independent institutions.The training-set cohort and the external validation-set cohort was comprised of 459 and 380 patients from each institution,respectively.The optimal cut-offvalue of SII was determined,and a prognostic risk stratification model was developed based on the training cohort and further assessed in the validation cohort.The propensity score matching(PSM)method was applied to minimize the confounding effects of unbalanced covariables.Results:The optimal cut-offvalue of the SII in the training cohort was 686,which was confirmed using the vali-dation cohort.Multivariate analysis showed that both before and after PSM,SII values>686 were independently associated with worse progression-free survival(PFS)ratio in both cohorts(before PSM,P=0.008 and P=0.008;after PSM,P=0.008 and P=0.007,respectively).Based on the analysis of independent prognostic factors of SII and N stage,we developed a categorical risk stratification model,which achieved significant discrimination among risk indexes associated with PFS and distant metastasis-free survival(DMFS)in the training cohort.There was no significant difference in PFS between RT alone and combined therapies within the low-and intermediate-risk groups(5-year PFS,77.5%vs.75.3%,P=0.275).Patients in the high-risk group who received concurrent chemoradiotherapy experienced superior PFS compared with those who received other therapies(5-year PFS,64.9%vs.40.3%,P=0.003).Conclusion:Pretreatment SII predicts PFS of patients with non-metastatic NPC.Prognostic risk stratification incorporating SII is instructive for selecting individualized treatment.