Background: Immunotherapy has improved the treatment landscape of mRCC pts and identifying biomarkers for patients’ selection is clinically needed. Inflammatory indices from peripheral blood showed a prognostic value in different tumors and therapies, including immunotherapy. These biomarkers are inexpensive and readily available in clinical practice. We aimed to assess the prognostic role of the dynamic evaluation of these indices in immunotherapy-naïve pretreated mRCC pts. Methods: The Meet-URO 15 multicentric retrospective study enrolled 571 pretreated mRCC pts receiving nivolumab. The Δ-Meet-URO was a secondary analysis on the early variation through the first four cycles of therapy compared with baseline (difference, delta - Δ) of white blood cells, platelets and inflammatory indices, including neutrophil-to-lymphocyte ratio (NLR), platelet-to-lymphocyte ratio (PLR) and systemic immune-inflammation index (SII, platelets x NLR), their comparison with baseline values and correlation with treatment response, overall (OS) and progression-free survival (PFS). The baseline and Δ cut-offs were identified by ROC curves for OS. Results: The analysis was performed on 422 mRCC pts (74% of the entire cohort). Patients with ΔNeutrophils < 730 at 2^nd, 3^rd and 4^th cycles were more responders (p< 0.001, p = 0.003 and p< 0.001) with longer mPFS (11 vs 6.1 months, p = 0.033) and mOS (46.9 vs 20.8 months, p = 0.046) compared to ΔNeutrophils ≥ 730. There was a significant interaction between baseline and ΔNeutrophils on PFS (p = 0.047). Pts with baseline neutrophils ≥ 4330/mm³ had longer mPFS when ΔNeutrophils < 730 (p = 0.002), whilst no difference was observed in those pts with baseline neutrophils < 4330/mm³ according to ΔNeutrophils (p = 0.46). Similar non-significant trends were observed in mOS. Patients with ΔNLR < 0.5 at 3^rd and 4^th cycles were more responders (p = 0.004 and p = 0.001, respectively) with doubled mPFS (12.1 vs 6.4 months, p = 0.007) and mOS (46.9 vs 21.7 months, p = 0.062) compared to ΔNLR ≥ 0.5. No significant interaction between baseline NLR and ΔNLR was observed in PFS and OS, suggesting a similar association between ΔNLR and PFS or OS, regardless of the baseline NLR cut-off of 3.2. The multivariable analyses confirmed all these results. Conclusions: The early assessment of NLR and neutrophils variations during immunotherapy for mRCC pts is a promising, affordable and non-invasive prognostic tool. Prospective and external validation analyses are warranted.