Prognostic Significance of Reverse Transcriptase Polymerase Chain Reaction for Prostate-Specific Antigen in Metastatic Prostate Cancer: A Nested Study Within CALGB 9583

Abstract

Purpose: To determine whether reverse transcriptase polymerase chain reaction (RT-PCR) to detect circulating prostate-specific antigen (PSA)-positive cells is a prognostic factor for survival in hormone refractory prostate cancer and to validate the prognostic importance of this test in relation to other known prognostic factors. Patients and Methods: A single centralized laboratory received and analyzed whole blood for RT-PCR for PSA for a subset of patients enrolled on two Cancer and Leukemia Group B (CALGB) randomized trials (CALGB 9583 and CALGB 9480). Using 9583, a prognostic model was developed and an independent data set (CALGB 9480) was used to validate the fitted model. Results: Of 162 patients in 9583, 91 (56%) patients were negative for RT-PCR for PSA and 71 (44%) patients were positive. The median survival time was 21 months (95% confidence interval [CI], 18 to 27 months) for RT-PCR-negative patients compared with 11 months (95% CI, 8 to 15 months) for RT-PCR-positive patients (P ≤ .001). In multivariable analysis, the hazard ratio (HR) for death was 1.7 (95% CI, 1.2 to 2.4; P = .006) for positive RT-PCR patients compared with negative RT-PCR patients. A fitted model that incorporated RT-PCR for PSA and other factors was used to classify patients from 9480 into one of two risk groups: low or high. We observed good agreement between the observed and predicted survival probabilities for the two risk groups. Conclusion: RT-PCR to detect PSA-positive circulating cells is confirmed to be a significant prognostic factor of survival in patients with hormone refractory prostate cancer. This model could be used to stratify patients in randomized phase III trials.