CT-measured tumor burden shows modest link to kidney function after partial nephrectomy

Three-dimensional measurements taken from preoperative CT scans may offer a more informative way to describe kidney tumors before surgery than the single maximum diameter that is conventionally reported, according to an exploratory analysis published in BMC Urology. The study, based on the public Kidney Tumor Segmentation Challenge 2023 training set, examined whether two CT-derived measures — tumor volume and a tumor burden ratio — were associated with kidney function after partial nephrectomy, and whether the burden ratio added information beyond the widely used maximum diameter.

The research was a retrospective secondary analysis of the KiTS23 dataset, which contains 489 cases. The investigators focused on patients who had undergone partial nephrectomy, a kidney-sparing operation, and who had both a preoperative estimated glomerular filtration rate, or eGFR, and a first postoperative eGFR measured between 90 and 365 days after surgery. The tumor burden ratio was defined as tumor volume divided by the combined volume of the kidney and the tumor, so it captures the extent of the tumor relative to the whole renal unit rather than in isolation.

From the dataset, 275 partial-nephrectomy cases were available, and 74 of those met the strict 90-to-365-day postoperative measurement criteria. The outcome of interest was the percentage decline in eGFR, a standard marker of kidney filtering capacity. The main analysis used linear regression adjusted for age, sex, body mass index, baseline eGFR, diabetes, and pre-existing chronic kidney disease, so the reported associations account for several established influences on postoperative renal function.

In the main analysis, each doubling of the tumor burden ratio was associated with a 2.83-percentage-point greater decline in eGFR, with a 95 percent confidence interval of 0.46 to 5.19 and a P value of 0.020. When the analysis was broadened to include all valid first postoperative measurements, regardless of the timing window, the estimate was smaller at 2.10 percentage points and was no longer statistically significant, with a confidence interval spanning from −0.09 to 4.29 and a P value of 0.060. The authors note that the estimate varied across analyses, a point they flag explicitly in their conclusions.

A key question the study set out to answer was whether the volumetric burden ratio tells clinicians anything that maximum tumor diameter does not. The two measures were strongly correlated, with a Spearman rho of 0.89, indicating that they capture largely overlapping information. Adding the tumor burden ratio to a model already containing maximum diameter increased the apparent R-squared by only 0.047, and the optimism-corrected R-squared by 0.034 — a modest incremental improvement in model fit.

The team also tested whether the relationship between tumor burden and functional decline followed a simple log2-linear form or departed from it. A spline analysis found no evidence of nonlinearity, with a P value of 0.928, although the authors caution that statistical power for this test was limited. They additionally examined how cohort selection, dataset composition, and tumor sphericity might have influenced the results, reflecting the exploratory nature of the work.

Because the KiTS23 training set includes cases that overlap with the earlier KiTS19 dataset as well as newly added cases, the researchers compared results between these subsets. The estimates differed between the KiTS19-overlap and additional KiTS23 subsets, but the interaction test was imprecise, with a P value of 0.314, meaning the data could not reliably establish whether the two subsets truly differed.

The authors conclude that the preoperative tumor burden ratio had a modest association with postoperative renal function, but that the estimate varied across analyses and its incremental contribution beyond maximum diameter remains uncertain. They emphasize that the measure describes tumor extent relative to the renal unit before surgery, and they call for independent cohorts with standardized renal assessment and postoperative parenchymal measurements before the ratio is used in clinical practice. As an exploratory, retrospective analysis of a public segmentation dataset, the findings should be read as hypothesis-generating rather than as a basis for changing surgical planning or patient counseling.

Subject of Research: The association between preoperative CT-derived renal tumor burden and postoperative kidney function after partial nephrectomy

Article Title: Preoperative CT-derived renal tumor burden and postoperative renal function after partial nephrectomy: an exploratory analysis of KiTS23

Article References: Liu, J., Guo, Z., Liu, K., Xing, S., & Liu, Q. (2026). Preoperative CT-derived renal tumor burden and postoperative renal function after partial nephrectomy: an exploratory analysis of KiTS23. BMC Urology. https://doi.org/10.1186/s12894-026-02378-w

Image Credits: AI Generated

DOI: 10.1186/s12894-026-02378-w

Keywords: partial nephrectomy, kidney tumor, tumor burden ratio, CT imaging, eGFR, renal function, KiTS23, retrospective analysis, maximum tumor diameter, urology, Preoperative, CT-derived