Background: The optimal number of 3-wk docetaxel plus prednisone (DP) cycles for metastatic castration-resistant prostate cancer (mCRPC) is unclear. Objective: A retrospective analysis of two clinical trials was performed to evaluate the association of the number of cycles with overall survival (OS). Design, setting, and participants: An exploratory analysis compared outcomes of 332 men who received DP in the TAX-327 trial, which stipulated up to 10 cycles, and 220 men who received DP in CS-205, a randomized phase 2 trial comparing DP plus AT-101 (bcl-2 inhibitor) versus DP plus placebo, which allowed up to 17 cycles. Measurements: Patients who completed 10 cycles of DP without progression in both trials were included. Men in both arms of CS-205 were combined for analysis, as no significant differences in outcomes were observed. OS was estimated from the date of cycle 10 docetaxel infusion. Results and limitations: The number of men receiving 10 cycles was similar (p = 0.26) in the two trials (166 [50.0%] in TAX-327 vs 99 [45.0%] in CS-205; the latter group received a median of five additional cycles). Six-and 12-mo estimated survival after cycle 10 was 92.2% (95% confidence interval [CI], 86.9-95.4%) and 74.6% (CI, 67.2-80.5%) in TAX-327, compared with 92.8% (CI, 85.5-96.5) and 63.4% (CI, 51.8-72.9%) in CS-205. Subanalyses suggested that <10 cycles may have a negative impact and p Conclusions: A survival benefit was not detected with >10 cycles of DP in men with mCRPC in this retrospective hypothesis-generating analysis. (C) 2011 European Association of Urology. Published by Elsevier B.V. All rights reserved.