The Fuhrman nuclear grade is the most widely used grading system for renal cell carcinoma. The aim of this study was to evaluate the intraobserver and interobserver variability of the Fuhrman and modified Fuhrman grading systems for conventional renal cell carcinoma. In this study, five pathologists independently classified 110 cases of conventional renal cell carcinoma according to the Fuhrman and modified (three- and two-tiered) Fuhrman grading systems. The intraobserver and interobserver variability of these systems were assessed using κ statistics. The associations between the Fuhrman and modified Fuhrman grades, pathologic stage and tumor size were determined by correlation analysis. The intraobserver and interobserver combined mean κ values for four-tiered Fuhrman grading were 0.48 and 0.41, respectively. The highest agreement was detected in two-tiered modification (including grades 1 + 2 and 3 + 4); the intraobserver and inter-observer combined mean κ values were 0.67 and 0.62, respectively. Correlations between pathologic stage and tumor size with two-tiered modification (including grades 1 + 2 and 3 + 4) were greater than those in three- and four-tiered Fuhrman grading. Collapsing the Fuhrman grading into a two-tiered scheme improved the intraobserver and interobserver reproducibility.
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