Purpose To investigate the prognostic role of the preoperative systemic immune–inflammation index (SII) in patients with upper tract urothelial carcinoma (UTUC) treated with radical nephroureterectomy (RNU). Materials and methods We retrospectively analyzed our multi-institutional database to identify 2492 patients. SII was calculated as platelet count × neutrophil/lymphocyte count and evaluated at a cutoff of 485. Logistic regression analyses were performed to investigate the association of SII with muscle-invasive and non-organ-confined (NOC) disease. Cox regression analyses were performed to investigate the association of SII with recurrence-free, cancer-specific, and overall survival (RFS/CSS/OS). Results Overall, 986 (41.6%) patients had an SII > 485. On univariable logistic regression analyses, SII > 485 was associated with a higher risk of muscle-invasive (P = 0.004) and NOC (P = 0.03) disease at RNU. On multivariable logistic regression, SII remained independently associated with muscle-invasive disease (P = 0.01). On univariable Cox regression analyses, SII > 485 was associated with shorter RFS (P = 0.002), CSS (P = 0.002) and OS (P = 0.004). On multivariable Cox regression analyses SII remained independently associated with survival outcomes (all P < 0.05). Addition of SII to the multivariable models improved their discrimination of the models for predicting muscle-invasive disease (P = 0.02). However, all area under the curve and C-indexes increased by < 0.02 and it did not improve net benefit on decision curve analysis. Conclusions Preoperative altered SII is significantly associated with higher pathologic stages and worse survival outcomes in patients treated with RNU for UTUC. However, the SII appears to have relatively limited incremental additive value in clinical use. Further study of SII in prognosticating UTUC is warranted before routine use in clinical algorithms.

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