Prognostic effect of preoperative systemic immune-inflammation index in patients treated with cytoreductive nephrectomy for metastatic renal cell carcinoma

BACKGROUND: Identifying those of patients with metastatic renal cell carcinoma (mRCC) who are most likely to benefit from cytoreductive nephrectomy (CN) is challenging. We tested the association between preoperative value of Systemic Immune-Inflammation Index (SII) and overall survival (OS) as well as cancer-specific survival (CSS) in mRCC patients treated with CN. METHODS: mRCC patients treated with CN at different institutions were included. After assessing for the optimal pretreatment SII cut‑off value, we found 710 to have the maximum Youden Index value. The overall population was therefore divided into two SII groups using this cut‑off (low, <710 vs. high, ≥710). Univariable and multivariable Cox regression analyses tested the association SII and OS as well as CSS. The discrimination of the model was evaluated with the Harrel's Concordance Index (C-Index). The clinical value of the SII was evaluated with decision curve analysis (DCA). RESULTS: Among 613 mRCC patients, 298 (49%) patients had a SII≥710. Median follow-up was 31 (IQR 16-58) months. On univariable analysis, high preoperative serum SII was significantly associated with worse OS (HR: 1.28, 95% CI: 1.07-1.54, P=0.01) and CSS (HR: 1.29, 95% CI: 1.08-1.55, P=0.01). On multivariable analysis, which adjusted for the effect of established clinicopathologic features, SII≥710 was associated with OS (HR: 1.25, 95% CI: 1.04-1.50, P=0.02) and CSS (HR: 1.26, 95% CI: 1.05-1.52, P=0.01). The addition of SII only slightly improved the discrimination of a base model that included established clinicopathologic features (C-index: 0.637 vs. 0.629). On DCA, the inclusion of SII did not improve the net-benefit of the prognostic model. On multivariable analyses, SII≥710 remained independently associated with the worse OS and CSS in IMDC intermediate risk group (both: HR: 1.31, 95% CI: 1.02-1.67, P=0.03). In the subgroup analyses based on the BMI, among patients with BMI ≥ 25, SII was significantly associated with OS (HR: 1.29, 95% CI: 1.04-1.61, P=0.02) and CSS (HR: 1.31, 95% CI: 1.05-1.63, P=0.02). CONCLUSIONS: We found an independent association of high SII prior to CN with unfavorable clinical outcomes, particularly in patients with intermediate risk mRCC and patients with increased BMI. Despite these results, it does not seem to add any prognostic or clinical benefit beyond that obtained by currently available clinicopathologic characteristics as sole worker.