External validation of the systemic immune-inflammation index as a prognostic factor in metastatic renal cell carcinoma and its implementation within the international metastatic renal cell carcinoma database consortium model.

BACKGROUND: We conducted a study to validate the influence of the systemic immune-inflammation index (SII) on overall survival (OS) in patients with metastatic renal cell carcinoma (mRCC) and to verify whether the implementation of the SII in place of neutrophil and platelet counts within the International Metastatic Renal Cell Carcinoma Consortium (IMDC) model might increase its prognostic accuracy. PATIENTS AND METHODS: We retrospectively analyzed consecutive patients with mRCC, who were treated with first-line tyrosine kinase inhibitors from 2008 to 2016 in two major oncology centres in Poland. We stratified patients into low SII (< 730) and high SII (≥ 730) groups according to a recent literature report. We used multivariable Cox proportional hazards regressions (CPHRs) to assess the impact of the SII on OS and concordance, global 'goodness-of-fit', calibration and reclassification measures to quantify a potential prognostic benefit from the modification of the IMDC model. RESULTS: Overall, 502 patients (294 with low and 208 with high SII) were included. Median OS was 36.7 months [95% confidence interval (CI) 30.4-41.5 months] and 17.0 months (95% CI 12.5-19.6 months) in the low and high SII groups, respectively. The SII status was significant in CPHRs with the hazard ratio ranging from 1.38 to 1.68. All prognostic accuracy measures favored the SII-modified-IMDC model over the original IMDC model. CONCLUSIONS: Using an external dataset, we showed that high SII was an independent factor for poor OS. The addition of the SII to the IMDC model in place of neutrophil and platelet counts increased the model's prognostic performance.