What is the clinical relevance of the Prostate Cancer Clinical Trials Working Group 2 (PCWG2) definition of radiographic progression-free survival (rPFS)?
In a series of prespecified sensitivity analyses of rPFS in the PREVAIL randomized clinical trial of 1717 men with chemotherapy-naive metastatic castration-resistant prostate cancer, enzalutamide significantly reduced the risk of radiographic progression or death. Using 2 different statistical methods, rPFS and overall survival were found to be positively correlated.
The PCWG2 definition of rPFS is a robust end point that is clinically meaningful and associated with overall survival.
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.
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.
Patients were randomized 1:1 to enzalutamide 160 mg 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.
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.
clinicaltrials.gov Identifier: NCT01212991
Rathkopf DE, Beer TM, Loriot Y, Higano CS, Armstrong AJ, Sternberg CN, de Bono JS, Tombal B, Parli T, Bhattacharya S, Phung D, Krivoshik A, Scher HI, Morris MJ. Radiographic Progression-Free Survival as a Clinically Meaningful End Point in Metastatic Castration-Resistant Prostate CancerThe PREVAIL Randomized Clinical Trial. JAMA Oncol. Published online March 08, 2018. doi:10.1001/jamaoncol.2017.5808
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