Prognostic Value of C-Reactive Protein–Albumin–Lymphocyte (CALLY) Index for Survival in Nivolumab-Treated Metastatic Renal Cell Carcinoma

Background and Objectives: Metastatic renal cell carcinoma (mRCC) remains a lethal disease despite advances with immune checkpoint inhibitors such as nivolumab. However, a substantial proportion of patients exhibit primary resistance or early progression, highlighting the need for reliable and easily accessible prognostic biomarkers. The C-reactive protein–albumin–lymphocyte (CALLY) index is a novel immunonutritional biomarker integrating systemic inflammation, nutritional status, and immune competence. Materials and Methods: In this retrospective single-center study, 91 patients with mRCC treated with nivolumab were analyzed. Patients were stratified into low and high CALLY index groups based on a receiver operating characteristic-derived cut-off (0.322). Survival outcomes were assessed using Kaplan–Meier analysis and Cox regression models. Results: Patients with a low CALLY index demonstrated significantly shorter progression-free survival (4.5 vs. 13.5 months, p < 0.001) and overall survival (9.1 vs. 25.5 months, p = 0.003). Multivariate analysis confirmed the CALLY index as an independent prognostic factor for both progression-free survival (HR: 2.63, p = 0.002) and overall survival (HR: 1.88, p = 0.035). Conclusions: The CALLY index is a simple, cost-effective, and reproducible biomarker that independently predicts survival in nivolumab-treated mRCC. It may serve as a practical tool for risk stratification and personalized treatment planning in the immunotherapy era.