External validation of the preoperative Karakiewicz nomogram in a large multicentre series of patients with renal cell carcinoma

Purpose: To perform a formal external validation of the preoperative Karakiewicz nomogram (KN) for the prediction of cancer-specific survival (CSS) using a large series of surgically treated patients diagnosed with organ-confined or metastatic renal cell carcinoma (RCC). Methods: Patient population originated from a series of retrospectively gathered cases that underwent radical or partial nephrectomy between years 1995 and 2007 for suspicion of kidney cancer. The original Cox coefficients were used to generate the predicted risk of CSS at 1, 2, 5, and 10 years following surgery and compared to the observed risk of CSS in the current population. External validation was quantified using measures of predictive accuracy, defined as model discrimination and calibration. Results: A total of 3,374 patients were identified. Relative to the original development cohort, the current sample population had a larger proportion of patients with localized (40.0 vs. 26.3 %, P < 0.001) and non-metastatic (92.2 vs. 88.1 %, P = 0.03) disease at presentation. Model discrimination for the prediction of CSS was 87.8 % (95 % CI, 84.4-91.4) at 1 year, 87.0 % (95 % CI, 84.4-89.5) at 2 years, 84.7 % (95 % CI, 82.3-87.1) at 5 years, and 85.9 % (95 % CI, 83.2-88.6) at 10 years. The relationship between predicted and observed CSS risk was adequate in the calibration plot. Conclusion: The use of the KN for the prediction of CSS in patients diagnosed with renal cell carcinoma was validated in the current study. In consequence, this tool may be recommended for routine clinical counseling in patients with various stages of RCC in the preoperative setting.