© The Canadian Journal of Urology™; 20(3); June 2013 Accepted for publication March 2013 Acknowledgment The international coordination of the European Randomized Study of Screening for Prostate Cancer (ERSPC) has been supported since the study’s initiation in 1991 by grants from Europe Against Cancer and the 5th and 6th framework program of the European Union, by many grants from agencies in the individual participating countries, and by unconditional grants from Beckman-Coulter-Hybritech Inc. Data referred to in this report are derived explicitly from the ERSPC Section Rotterdam, which is supported by grants from the Dutch Cancer Society, The Netherlands Organisation for Health Research and Development, the Abe Bonnema Overestimation of prostate cancer mortality and other-cause mortality by the Kaplan-Meier method Xiaoye Zhu, MD, Ries Kranse, PhD, Meelan Bul, MD, Chris H. Bangma, MD, Fritz. H. Schröder, MD, Monique J. Roobol, PhD Department of Urology, Erasmus University Medical Center, Rotterdam, The Netherlands ZHU X, KRANSE R, BUL M, BANGMA CH, SCHRÖDER FH, ROOBOL MJ. Overestimation of prostate cancer mortality and other-cause mortality by the Kaplan-Meier method. Can J Urol 2013;20(3): 6756-6760. Introduction: To assess the extent of overestimation of the cumulative probability of death by the Kaplan-Meier method with the competing-risks regression analysis as reference approach. Materials and methods: Data were derived from the screening arm of the Rotterdam branch of the European Randomized Study of Screening for Prostate Cancer (ERSPC). The screening arm consisted of 21210 men between the ages of 55 and 74 at study entry. Follow up concerning mortality was complete through 2008. Endpoints were 5 and 10 year cumulative probabilities of prostate cancer death and death from other causes. Relative bias was deined as the ratio of the cumulative probability of death as determined by the Kaplan-Meier method, relative to the cumulative probability obtained by the competing-risks analysis. Results: According to the Kaplan-Meier method, the 5 year cumulative probability of death from prostate cancer was 0.0101, compared with 0.0099 according to the competing-risk analysis [1.8% overestimation]. At 10 year, these numbers were 0.0347 and 0.0321, respectively [8.0% overestimation]. For death from other causes, the cumulative probabilities at 5 year were 0.0399 and 0.0397 according to the Kaplan-Meier and the competing-risks method [0.6% overestimation], respectively. At 10 year, the probabilities were 0.141 and 0.139 [1.7% overestimation], respectively. Conclusions: When competing events are present, the competing-risks regression analysis is to be preferred over the Kaplan-Meier method in the estimation of the cumulative probability of the event of interest. Key Words: competing-risks regression analysis, Kaplan-Meier estimate, other-cause mortality, prostate cancer mortality, prostate cancer screening, European Randomized Study of Screening for Prostate Cancer 6756 Foundation and by many private donations. The authors also thank JBW Rietbergen, A Boeken-Kruger, GJ de Zwart, IW van der Cruijsen-Koeter, MO Boerma, A Prins, R Raaijmakers, and SH de Vries for performing the DRE/TRUS and prostate biopsies during the initial and repeat screening of ERSPC Rotterdam. CGAM Franken-Raab, DW Roobol, and M van Slooten-Midderigh are acknowledged for data collection and data entry. Address correspondence to Dr. Xiaoye Zhu, Department of Urology, Erasmus MC, University Medical Center Rotterdam, Room NH-227, PO Box 2040, 3000 CA Rotterdam, The Netherlands