Radiographic Progression-Free Survival as a Clinically Meaningful End Point in Metastatic Castration-Resistant Prostate Cancer - the PREVAIL Randomized Clinical Trial

IMPORTANCE: Drug development for metastatic castration-resistant prostate cancer has been limited by a lack of clinically relevant trial end points short of overall survival (OS). Radiographic progression-free survival (rPFS) as defined by the Prostate Cancer Clinical Trials Working Group 2 (PCWG2) is a candidate end point that represents a clinically meaningful benefit to patients.

OBJECTIVE: To demonstrate the robustness of the PCWG2 definition and to examine the relationship between rPFS and OS.

DESIGN, SETTING, AND PARTICIPANTS: PREVAIL was a phase 3, randomized, double-blind, placebo-controlled multinational study that enrolled 1717 chemotherapy-naive men with metastatic castration-resistant prostate cancer from September 2010 through September 2012. The data were analyzed in November 2016.

INTERVENTIONS: Patients were randomized 1:1 to enzalutamide 160mg or placebo until confirmed radiographic disease progression or a skeletal-related event and initiation of either cytotoxic chemotherapy or an investigational agent for prostate cancer treatment.

MAIN OUTCOMES AND MEASURES: Sensitivity analyses (SAs) of investigator-assessed rPFS were performed using the final rPFS data cutoff (May 6, 2012; 439 events; SA1) and the interim OS data cutoff (September 16, 2013; 540 events; SA2). Additional SAs using investigator-assessed rPFS from the final rPFS data cutoff assessed the impact of skeletal-related events (SA3), clinical progression (SA4), a confirmatory scan for soft-tissue disease progression (SA5), and all deaths regardless of time after study drug discontinuation (SA6). Correlations between investigator-assessed rPFS (SA2) and OS were calculated using Spearman ρ and Kendall τ via Clayton copula.

RESULTS: In the 1717 men (mean age, 72.0 [range, 43.0-93.0] years in enzalutamide arm and 71.0 [range, 42.0-93.0] years in placebo arm), enzalutamide significantly reduced risk of radiographic progression or death in all SAs, with hazard ratios of 0.22 (SA1; 95%CI, 0.18-0.27), 0.31 (SA2; 95%CI, 0.27-0.35), 0.21 (SA3; 95%CI, 0.18-0.26), 0.21 (SA4; 95%CI, 0.17-0.26), 0.23 (SA5; 95%CI, 0.19-0.30), and 0.23 (SA6; 95%CI, 0.19-0.30) (P < .001 for all). Correlations of rPFS and OS in enzalutamide-treated patients were 0.89 (95%CI, 0.86-0.92) by Spearman ρ and 0.72 (95%CI, 0.68-0.77) by Kendall τ.

CONCLUSIONS AND RELEVANCE: Sensitivity analyses in PREVAIL demonstrated the robustness of the PCWG2 rPFS definition using additional measures of progression. There was concordance between central and investigator review and a positive correlation between rPFS and OS among enzalutamide-treated patients.

JAMA Oncol. doi:10.1001/jamaoncol.2017.5808. Published online March 8, 2018.

Authors: Dana E. Rathkopf, MD1; Tomasz M. Beer, MD2; Yohann Loriot, MD, PhD3; Celestia S. Higano, MD4; Andrew J. Armstrong, MD, ScM5; Cora N. Sternberg, MD6; Johann S. de Bono, MB ChB, PhD7; Bertrand Tombal, MD, PhD8; Teresa Parli, MD9,10; Suman Bhattacharya, PhD10; De Phung, BSc11; Andrew Krivoshik, MD, PhD12; Howard I. Scher, MD1; Michael J. Morris, MD1

Author Information: 

1. Genitourinary Oncology Service, Department of Medicine, Memorial Sloan Kettering Cancer Center andWeill Cornell Medicine, New York, New York
2. Department of Hematology/Medical Oncology, OHSU Knight Cancer Institute, Oregon Health and Science University, Portland 
3. Gustave Roussy, Cancer Campus, Department of Cancer Medicine, University of Paris Saclay, Villejuif, France
4. Department of Medical Oncology, University of Washington and Fred Hutchinson Cancer Research Center, Seattle,Washington
5. Divisions of Medical Oncology andUrology, Duke University Medical Center, Duke Cancer Institute, Duke University, Durham, North Carolina 
6. Department of Medical Oncology, San Camillo and Forlanini Hospitals, Rome, Italy
7. Division of Clinical Studies, Royal Marsden Hospital and Institute of Cancer Research, London, England
8. Division of Urology, Cliniques Universitaires Saint-Luc, Brussels, Belgium 
9. Department of Clinical Development, Medivation, LLC, a Pfizer company, San Francisco, California 
10. formerly with Department of Biostatistics, Medivation, LLC, a Pfizer company, San Francisco, California
11. Department of Biostatistics, Astellas Pharma Europe BV, Leiden, The Netherlands
12. Department of Medical Oncology, Astellas Pharma, Inc, Northbrook, Illinois

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