Risk stratification by pathological upstaging and tumor necrosis in clinical T1 clear-cell renal cell carcinoma: evidence from a multi-institutional cohort of 1081 patients

PURPOSE: To identify independent prognostic factors for recurrence and develop a practical risk stratification system in patients with clinical T1 (cT1) clear-cell renal cell carcinoma (ccRCC) following curative-intent surgery. METHODS: This retrospective multi-institutional study analyzed 1081 consecutive patients with cT1N0M0 ccRCC who underwent partial or radical nephrectomy at 14 Japanese tertiary centers (2016-21). We evaluated six established prognostic factors based on prior literature: pathological T3 upstaging, tumor size, nuclear grade, tumor necrosis, surgical approach, and venous invasion. Cox proportional hazards regression was performed to identify independent predictors of recurrence-free survival. RESULTS: During a median follow-up of 48 months, 66 patients (6.1%) developed recurrence. Multivariable Cox regression identified two independent prognostic factors: pathological T3 upstaging (HR 4.67, 95% CI 2.40-9.08, P