Association of Pathological Tumor-to-kidney Volume Ratio with Adverse Pathological Features After Radical Nephrectomy: An Exploratory Retrospective Cohort Study

Objective: To evaluate the association of the pathology-derived tumor-to-kidney volume ratio (T/K ratio) with adverse pathological features and assess whether it provides prognostic information for cancer-specific survival (CSS) beyond maximum tumor diameter in renal cell carcinoma (RCC) patients undergoing radical nephrectomy. Materials and Methods:We retrospectively reviewed the records of 151 patients who underwent radical nephrectomy for non-metastatic RCC between 2005 and 2018.Tumor and kidney volumes were calculated from three orthogonal dimensions measured pathologically using the ellipsoid formula.An exploratory data-derived T/K ratio cut-off of 0.45 was used for group comparisons.Associations were evaluated using group comparisons, Spearman correlation, Kaplan-Meier analysis, and a parsimonious Cox model (T/K ratio and maximum tumor diameter), with CSS as the primary endpoint.Results: The high T/K ratio group (n=28) had a greater tumor diameter than the low-ratio group (8.5 vs. 5.0 cm; p<0.001) and higher frequencies of renal vein involvement, microvascular invasion, tumor necrosis, collecting system invasion, and positive surgical margins (all p<0.05).The T/K ratio correlated strongly with tumor volume (ρ=0.789) and maximum diameter (ρ=0.747),but not with kidney volume (ρ=0.089).Median follow-up was 73 months [95% confidence interval (CI), 62-86)].Five-year CSS was 66.9% (95% CI, 42.2-82.9%) in the high-ratio group and 94.7% (95% CI, 87.6-97.8%) in the low-ratio group (p<0.001).In the parsimonious model, the T/K ratio was not independently associated with cancer-specific mortality after adjustment for diameter [hazard ratio (HR) per 0.10 increase, 1.14; 95% CI, 0.90-1.44;p=0.262], whereas diameter remained significant (HR per 1 cm, 1.21; 95% CI, 1.03-1.41;p=0.022).Conclusion: A high T/K ratio was associated with adverse pathological findings and inferior unadjusted survival, but showed no independent association with cancer-specific mortality after adjustment for maximum tumor diameter.The ratio should be considered an exploratory morphometric index.