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Prostate-Specific Antigen and Pain Surrogacy Analysis in Metastatic Hormone-Refractory Prostate Cancer

Andrew J. Armstrong, Elizabeth Garrett-Mayer, Yi-Chun Ou Yang, Michael A. Carducci, Ian Tannock, Ronald de Wit, Mario Eisenberger

From the Duke Comprehensive Cancer Center, Durham, NC; Sidney Kimmel Comprehensive Cancer Center, Johns Hopkins School of Medicine, Baltimore, MD; Department of Medical Oncology, Princess Margaret Hospital and University of Toronto, Toronto, Ontario, Canada; and the Department of Medical Oncology, Rotterdam Cancer Institute, Erasmus University Medical Center, Rotterdam, the Netherlands

Address reprint requests to Andrew J. Armstrong, MD, ScM, DUMC Box 3850, Durham, NC 27710; e-mail: andrew.armstrong{at}duke.edu

Purpose: It is currently unclear if early prostate-specific antigen (PSA) or pain improvements are adequate surrogates for overall survival in men with metastatic hormone-refractory prostate cancer (HRPC). Here we examined various degrees of PSA decline and pain response as surrogates for the survival benefit observed in the TAX327 trial.

Patients and Methods: In the TAX327 trial, 1,006 men with HRPC were randomly assigned to receive docetaxel in two schedules, or mitoxantrone, each with prednisone: 989 men provided data on 3-month PSA decline. Surrogacy was examined for post-treatment changes in PSA and pain response using Cox proportional hazards models to calculate the proportion of treatment effect (PTE) explained by each potential surrogate.

Results: A 30% PSA decline within 3 months of treatment initiation provides the highest degree of surrogacy, with a PTE of 0.66 (95% CI, 0.23 to 1.0), and was associated with a hazard ratio (HR) of 0.50 (95% CI, 0.43 to 0.58) for overall survival after adjusting for treatment effect. Introduction of a 30% PSA decline is predictive of survival regardless of treatment arm. Other changes in PSA or PSA kinetics, PSA normalization, and pain responses were highly prognostic but weaker surrogates for survival.

Conclusion: In the TAX327 trial, a PSA decline of 30% within 3 months of chemotherapy initiation had the highest degree of surrogacy for overall survival, confirming data from the Southwest Oncology Group 9916 trial. However, given the wide CIs around the estimate of this moderate surrogate effect, overall survival should remain the preferred end point for phase III trials of cytotoxic agents in HRPC.

Authors' disclosures of potential conflicts of interest and author contributions are found at the end of this article.

Related Correspondence

• Are Prostate-Specific Antigen Changes Valid Surrogates for Survival in Hormone-Refractory Prostate Cancer? A Meta-Analysis Is Needed!
  Laurence Collette, Marc Buyse, and Tomasz Burzykowski
  JCO 2007 25: 5673-5674 [Full Text]

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