The Fuhrman system is the most widely used nuclear grading system for renal cell carcinoma (RCC). Although Fuhrman nuclear grade is widely accepted as a significant prognostic factor, its reproducibility, as reported in the limited number of series available in the literature, appears to be low.
Between 1980 and 1990, 255 cases of RCC (pT1–3bN0M0) were treated with radical nephrectomy at the Department of Urology, University Hospital, Strasbourg, France. In a retrospective multicenter study, 3 pathologists independently classified 241 of these 255 cases according to the Fuhrman grading system. The authors searched for optimal interobserver agreement by collapsing the grading system to a three-tiered scheme and then to a two-tiered scheme. In addition, overall survival curves were generated according to the classic four-tiered scheme and also according to the best collapsed scheme. The kappa index was used to assess the level of agreement between each pair of observers, and the Cox model was used for multivariate survival analyses.
The mean interobserver κ value was 0.22 (range, 0.09–0.36). The best concordance was obtained by collapsing to a system in which low-grade (Grade 1–2) disease was compared with high-grade (Grade 3–4) disease. Doing so improved the mean interobserver κ value to 0.44 (range, 0.32–0.55). Fuhrman grade was an independent prognostic factor for all 3 pathologists (P = 0.01, P < 0.0001, and P = 0.004, respectively), and nuclear grade continued to have independent prognostic value after the optimal collapsing algorithm was performed (P = 0.004, P = 0.0003, and P = 0.005).
Collapsing of the Fuhrman grading system to a two-tiered scheme led to an improvement in interobserver agreement while preserving the independent prognostic value of nuclear grade. Cancer 2005. © 2004 American Cancer Society.