External Validation of the Mayo Clinic Stage, Size, Grade and Necrosis (SSIGN) Score to Predict Cancer Specific Survival Using a European Series of Conventional Renal Cell Carcinoma

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Abstract
We validated the Mayo Clinic SSIGN score in an independent European sample of patients who were surgically treated for conventional RCC. In our kidney cancer database we identified 388 patients who were treated with radical or partial nephrectomy for conventional RCC between 1986 and 2000. Associations of the pathological features studied with death from RCC were evaluated using the log rank test and Cox proportional hazards regression model. The predictive ability of competing models was evaluated using the c index. Median followup in the 290 patients who were alive at last followup was 5 years (range 5 months to 17 years). The estimated cancer specific survival rate 5 years following surgery was 81.3%. All features that comprise the SSIGN score except tumor size were significantly associated with death from RCC in a multivariate setting, resulting in a c index of 0.90. The median SSIGN score in the 388 patients studied was 3 (range 0 to 15). The c index in a model containing the clear cell SSIGN score was 0.88. Five-year cancer specific survival rates in patients with a score of 0 to 2, 3 to 4, 5 to 6, 7 to 9 and 10 or more were 100.0%, 90.5%, 63.6%, 46.8% and 0%, respectively. We provide the first external validation of the Mayo Clinic SSIGN score for conventional RCC. This simple algorithm resulted in a high degree of prognostic accuracy.