External validation of disease-free survival at 2 or 3 years as a surrogate and new primary endpoint for patients undergoing radical cystectomy for urothelial carcinoma of the bladder

Purpose: To perform the first external validation of a recently identified association between disease-free survival at two years (DFS2) or three years (DFS3) and overall survival at five years (OS5) in patients after radical cystectomy (RC) for muscle-invasive urothelial carcinoma of the bladder (UCB). Methods and Methods: Records of 2483 patients who underwent RC for UCB at eight European centers between 1989 and 2008 were reviewed. The cohort included 1738 patients with pT2-4a tumors and negative soft tissue surgical margins (STSM) according to the selection criteria of the previous study (study group (SG)). In addition, 745 patients with positive STSM or other tumor stages (pT0-T1, pT4b) that were excluded from the previous study (excluded patient group (EPG)) were evaluated. Kappa statistic was used to measure the agreement between DFS2 or DFS3 and OS5. Results: The overall agreement between DFS2 and OS5 was 86.5% (EPG: 88.7%) and 90.1% (EPG: 92.1%) between DFS3 and OS5. The kappa values for comparison of DFS2 or DFS3 with OS5 were 0.73 (SE: 0.016) and 0.80 (SE: 0.014) respectively for the SG, and 0.67 (SE: 0.033) and 0.78 (SE: 0.027) for the EPG (all p-values <0.001). Conclusions: We externally validated a correlation between DFS2 or DFS3 and OS5 for patients with pT2-4a UCB with negative STSM that underwent RC. Furthermore, this correlation was found in patients with other tumor stages regardless of STSM status. These findings indicate DFS2 and DFS3 as valid surrogate markers for survival outcome with RC.