Exploring the role of the systemic immune-inflammation index in colorectal cancer: A study on screening and prognostic assessment

Abstract

BACKGROUND

Colorectal cancer (CRC) remains a leading cause of cancer-related mortality worldwide, making early detection of precancerous adenomas critical for effective prevention. The systemic immune-inflammation index (SII), derived from peripheral blood counts, reflects the balance between inflammation and immune surveillance. However, its role in distinguishing CRC from adenomas and its prognostic value remain unclear.

AIM

To investigate the clinical utility of SII in screening for CRC and precancerous adenomas, and to evaluate its association with pathological features and prognosis.

METHODS

This retrospective study included 332 patients (141 with CRC, 191 with colorectal adenoma) who underwent colonoscopy between January 2019 and June 2025. Peripheral blood-based indices including SII, neutrophil-to-lymphocyte ratio (NLR), platelet-to-lymphocyte ratio (PLR), and C-reactive protein (CRP) were calculated. Receiver operating characteristic curves determined optimal cut-offs for CRC diagnosis and lymph node metastasis prediction. Multivariate logistic regression identified independent risk factors. Survival was analyzed using Kaplan-Meier methods.

RESULTS

SII was significantly higher in CRC than that in adenomas [712.76 (IQR: 435.87-1586.92) vs 347.56 (IQR: 256.05-471.03), P < 0.001]. The optimal SII cut-off for distinguishing CRC from adenoma was 480.326 [area under the curve (AUC) = 0.801, sensitivity 72.3%, specificity 76.1%]. Multivariate logistic regression confirmed that elevated SII [per 100-unit increase: Odds ratio (OR) = 1.195, 95% confidence interval: 1.101-1.298, P < 0.001], NLR (OR = 1.489, P < 0.001), PLR (OR = 1.009, P < 0.001), and CRP (OR = 1.069, P = 0.003) were independent risk factors for CRC after adjusting for age, hemoglobin, carcinoembryonic antigen, and fecal immunochemical test. For predicting lymph node metastasis, the optimal SII cut-off was 411.93 (AUC = 0.682). High SII was significantly associated with advanced T stage (P = 0.009), lymph node metastasis (P = 0.027), and vascular/neural invasion (P = 0.039). During follow-up, 8 deaths occurred. The high-SII group showed a trend toward lower overall survival (0% vs 11.8% mortality, P = 0.076), but this did not reach statistical significance.

CONCLUSION

Elevated SII is an independent risk factor for CRC and may serve as a useful auxiliary screening marker. Preoperative SII correlates with aggressive pathological features, however, its prognostic value requires validation in larger prospective cohorts with longer follow-up.

Keywords: Colorectal adenoma; Colorectal cancer; Systemic immune inflammatory index; Screening; Prognosis

Core Tip: This retrospective study explored the clinical value of systemic immune-inflammation index (SII) screening and assessing colorectal adenoma and colorectal cancer (CRC). Receiver operating characteristic curve determined SII’s diagnostic threshold for CRC and precancerous lesions as 480.326. Elevated SII was identified as an independent risk factor for CRC, but preoperative SII has no significant correlation with CRC patients’ overall survival.