Establishment and validation of a prognostic model associated with systemic immune inflammatory index (SII) before neoadjuvant chemoradiotherapy in locally advanced rectal cancer

Abstract Purpose: The aim of this study is to investigate the effect of systemic immune inflammation index (SII) on the prognosis, and to determine whether the combination of SII and traditional risk factors could enhance prognosis prediction of locally advanced rectal cancer (LARC). Methods and Materials: We retrospectively reviewed the clinical data of 288 patients with LARC. Clinical variables and hematological parameters of peripheral blood of patients before neoadjuvant chemoradiotherapy were incorporated into further analyses. The primary endpoint was overall survival (OS). According to LASSO penalized Cox and multivariate Cox regression analyses, four independent prognostic risk factors were screened to constructed tow prognostic models and have verified the role of SII in the model. The ROC curve (Receiver operating characteristic ) was applied to determine the optimal cut-off values for SII, and then according to the optimal cut-off value, LARC patients were divided into high- and low-SII groups to perform Kaplan-Meier survival analysis and log-rank tests. Results: Multivariate cox regression (stepwise method) analysis revealed that SII, cN, radiotherapy regimen and received surgery were independent prognostic risk factors. The nomogram model based on the four factors showed that SII shared the largest contributions to prognosis, followed by surgery, cN staging and radiotherapy regimen. The nomogram including SII (AIC, 621.17; C‑index, 0.778) possessed superior prognostic value compared with the nomogram without SII (AIC, 628.35; c-index,0.756). The optimal cut-off value of SII was 587.03 for predicting OS yielded by ROC curve analysis. KM survival analysis showed that the survival of patients with low SII was significantly better than that of patients with high SII (p＜0.0001). Conclusions: The levels of SII before neoadjuvant chemoradiotherapy have important predictive value for the prognosis of patients with LARC, and combining SII with the traditional risk factors may improve predictive performance.