Purpose: The incidence of accidentally detected small renal tumors is increasing throughout the world. In this multi-institutional study performed in Korea, histopathological characteristics of contemporarily surgically removed renal tumors were reviewed with emphasis on tumor size. Materials and Methods: Between January 1995 and May 2005, 1,702 patients with a mean age of 55 years underwent surgical treatment at 14 training hospitals in Korea for radiologically suspected malignant renal tumors. Clinicopathological factors and patient survival were analyzed. Results: Of the 1,702 tumors, 91.7% were malignant and 8.3% were benign. The percentage of benign tumors was significantly greater among those ≤ 4cm (13.2%) than those >4cm (4.5%) (p<0.001). Among renal cell carcinoma patients, the percentage of tumors classed as stage >T3 was significantly less among tumors ≤ 4cm (5.2%) than those >4cm (26.8%) (p<0.001). The percentage of tumors classed as Fuhrman's nuclear grades 3 was also significantly less among tumors ≤ 4 cm (27.3%) than tumors >4 cm (50.9%) (p<0.001). The 5-year cancer-specific survival rate was 82.7%, and T stage (p < 0.001), N stage (p < 0.001), M stage (p= 0.025), and Fuhrman's nuclear (p<0.001) grade were the only independent predictors of cancer-specific survival. Conclusion: In renal tumors, small tumor size is prognostic for favorable postsurgical histopathologies such as benign tumors, low T stages, and low Fuhrman's nuclear grades. Our observations are expected to facilitate urologists to adopt function-preserving approach in the planning of surgery for small renal tumors with favorable predicted outcomes.
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