P37 Impact of surgical margins on overall and cancer-specific survival in kidney cancer patients

Introduction & Objectives: Nephron spearing surgery (NSS) is the primary treatment option for localized renal cell carcinoma, aiming to remove the tumor while preserving kidney function. The goal of surgery is to achieve clean resection margins, as positive margins are believed to increase recurrence risk. However, their impact on overall survival (OS) and cancer-specific survival (CSS) remains debated. Materials & Methods: This study included 964 patients who underwent NSS at a tertiary university center (2012-2023). The primary endpoints were OS and CSS, measured from the date of surgery to the last follow-up or death. Kaplan-Meier curves were used to estimate 10-year OS and CSS rates. Survival differences between patients with positive (R1) and negative (R0) surgical margins were assessed using the log-rank test. Clinical and pathological factors were compared between groups using the Chi-square and Mann-Whitney test. Multivariate Cox regression analysis was performed to identify factors associated with OS and CSS. A p-value < 0.05 was considered statistically significant. Results: Of the 946 patients, 222 (23%) had benign tumors. Among the 742 patients included in the study, 57.28% were male, with a median age of 64 years (IQR 57–71). The median tumor size was 3.1 cm (IQR 2.3– 4.0), and the most common histological subtype was clear cell renal carcinoma (78.97%), followed by papillary renal carcinoma (10.78%) and chromophobe renal carcinoma (8.22%). The majority of tumors were classified as grade G2 (71.1%). R1 resection status was observed in 92 cases (12.2%). During the follow-up period (median: 60.25 months), 111 patients (14.7%) died, with 29 (3.9%) deaths attributed to renal cancer. The 10-year OS rate for the entire cohort was 73.3%, while the CSS rate was 93.2%. No differences in baseline characteristics were found between the R1 and R0 groups. The 10-year OS was 74.4% in the R0 group and 59.1% in the R1 group (p=0.3), while the 10-year CSS was 93.9% and 86.7% (p=0.5), respectively. Multivariate Cox regression analysis did not confirm R1 status as an independent predictor of worse survival (OS: HR=1.4 95% CI:0.77–2.51, p=0.3; CSS: HR=1.7, 95% CI:0.57–5.09, p=0.3). OS was significantly influenced by patient age (HR=1.05, 95% CI: 1.03–1.07, p<0.001) and tumor differentiation grade. A significant difference in OS was observed when comparing G1 and G2 groups (HR=1.9, 95% CI:1.01–3.46, p=0.046), with an even more pronounced effect between G1 and G3 (HR=2.5, 95% CI:1.07–5.74, p=0.03). CSS was also affected by age (HR=1.06, 95% CI:1.02–1.10, p=0.005) and tumor differentiation grade, particularly in the G3 group compared to G1 (HR=8.6, 95% CI:1.75–42.26, p=0.008). Conclusions: R1 status was linked to lower 10-year OS and CSS, but not significantly. Age and tumor differentiation grade were the strongest predictors of survival, while surgical margin status had no significant impact.