Disease-free survival at 2 and 3 years is a significant early surrogate marker predicting the 5-year overall survival in patients treated with radical cystectomy for urothelial carcinoma of the bladder: External evaluation and validation in a cohort of Korean patients

Purpose: We aimed to externally validate the association of 2- and 3-year disease-free survival (DFS) with 5-year overall survival (OS) in patients treated with radical cystectomy (RC) for urothelial carcinoma (UC) of the bladder. Materials and Methods: We reviewed the clinical data of 422 patients who underwent RC for UC of the bladder in our institution between 1991 and 2012. Survival curves were plotted with the Kaplan-Meier method. The Kappa statistic and Kendall tau-b test were used to assess the agreements between 2- and 3-year DFS and 5-year OS. Results: In the entire study population, 2- and 3-year DFS and 5-year OS rates were 76.4, 71.5, and 67.4%, respectively. All Kappa and Kendall's tau-b test values for agreements between 2- and 3-year DFS and 5-year OS were more than 0.40, indicating moderate agreement for all patients and in each patient subgroup selected according to specific variables (all p-values < 0.05). Kaplan-Meier analysis for DFS and Cox-proportional hazard models for landmark analysis at each time point indicated that most recurrences occurred within 3 years after surgery. The 5-year OS rates of patients who were recurrence-free at each time point gradually increased to more than 95% in an extended recurrence-free interval of 12-36 months. Conclusion: Our external validation results support the existing finding that 2- and 3-year DFS can be a valid early surrogate end point to predict 5-year OS after RC in patients with UC of the bladder.