Elevated B12/CRP Index as a Simple Prognostic Indicator in Patients with Metastatic Renal Cell Carcinoma Treated with First-Line Targeted Therapy

Background/Objectives: The vitamin B12 (VB12)/C-reactive protein (CRP) index (BCI), a clinically derived index calculated as serum VB12 multiplied by CRP, has shown prognostic value in several cancers. However, its association with survival outcomes in metastatic renal cell carcinoma (mRCC) remains unclear. Therefore, the aim of the present study was to evaluate the prognostic significance of BCI in patients with mRCC treated with targeted therapy. Methods: The BCI was calculated as serum VB12 concentration (pg/mL) × serum CRP concentration (mg/L). The patients were categorized into two BCI prognostic subgroups, high BCI (BCI > 40,000) and low BCI (≤40,000). Survival differences between prognostic subgroups were measured using the Kaplan–Meier method with a log-rank test. Univariate and multivariable analyses were used to determine the association between the selected variables and survival outcomes. Results: We included 213 patients with mRCC, with a median follow-up time of 76 months. The median progression-free survival (PFS) and overall survival (OS) were 10.9 months and 47.7 months, respectively. Patients with high BCI had poorer PFS and OS times than those with low BCI (7.8 months vs. 12.6 months, p = 0.002 for PFS; 22.6 months vs. 68 months, p < 0.001 for OS, respectively). After adjusting for potential confounders, high BCI remained independently associated with poorer PFS and OS (hazard ratio [HR]: 2.40, 95% confidence interval [CI] 1.35–4.26, p = 0.003 for PFS; HR 2.01, 95% CI 1.40–2.88, p < 0.001 for OS). Conclusions: BCI appears to be a promising prognostic biomarker in patients with mRCC treated with first-line targeted therapy. However, its applicability to immune checkpoint inhibitor-based or combination regimens requires prospective validation.