Cross-cultural validation of a prognostic tool: example of the Kattan preoperative nomogram as a predictor of prostate cancer recurrence after radical prostatectomy.

Abstract

To establish the predictive accuracy of the Kattan preoperative nomogram by comparing predictions at 5 years with actual progression in patients who had a radical prostatectomy (RP). We reviewed the data for 928 patients treated by RP as a first-line treatment for localized prostate cancer, between 1994 and 2005. Recurrence was defined as one prostate-specific antigen (PSA) level of >0.4 ng/mL. The 5-year progression-free probability (PFP) rate was evaluated on censured data using the Kaplan-Meier method. Relationships between all predictor variables included in the Kattan nomogram (PSA level, biopsy Gleason scores and clinical stage) and survival were evaluated by Cox proportional-hazards regression analysis. The discriminating ability of the nomogram was assessed by the concordance index (c-index). Bootstrapping was used to assess confidence intervals (CIs), and then the calibration was assessed. The median follow-up was 60 months. Overall, 177 (19%) patients had a recurrence; the 5-year PFP rate (95% CI) was 80.9 (78-83)%. Of the three variables included in the nomogram, all were associated with recurrence in a multivariate analysis (P < 0.001). The c-index (95% CI) was only 0.664 (0.584-0.744). In general, the nomogram was not well calibrated. There was a discrepancy between the predicted PFP as estimated by the Kattan nomogram and actual relapse in this group of patients. Clinicians should be aware that the nomogram is less accurate when used outside the population used to formulate the nomogram. Although more accurate tools are needed, the Kattan nomogram is still the best choice for urologists so far.