PROSTATE SPECIFIC ANTIGEN RESPONSE TO MITOXANTRONE AND PREDNISONE IN PATIENTS WITH REFRACTORY PROSTATE CANCER: PROGNOSTIC FACTORS AND GENERALIZABILITY OF A MULTICENTER TRIAL TO CLINICAL PRACTICE

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Abstract
Purpose: We determine prostate specific antigen (PSA) response and durability, and prognostic factors associated with response and survival in patients with symptomatic hormone refractory prostate cancer treated with mitoxantrone and prednisone at a single institution. We then compare the results with those of a randomized phase III clinical trial. Materials and Methods: A retrospective review of all 133 patients treated with mitoxantrone and prednisone at Princess Margaret Hospital since 1994 was performed. PSA response and duration, and overall survival were determined as well as the influence of baseline factors on these outcome parameters. Results were compared to those for patients randomized to receive mitoxantrone and prednisone in the Canadian clinical trial which demonstrated palliative benefit of this regimen. Results: Patients treated after trial closure had shorter survival (p = 0.003) but represented a poorer prognosis cohort. PSA response of the trial and post-trial cases was 34% and 28%, respectively (p = 0.36), and median duration of response was 118 and 175 days or greater, respectively. Factors predictive of PSA response in the nontrial cohort were longer time from diagnosis of prostate cancer (p = 0.027) and higher baseline PSA (p = 0.013). Factors predictive of increased survival in both groups were younger age (p <0.04), better baseline Eastern Cooperative Oncology Group performance status (p <0.02), and higher hemoglobin (p ≤0.05) and PSA response (p <0.0001). Gleason score was not predictive of response or survival. Conclusions: Although patients treated outside of the trial had poorer prognostic features, rates of PSA response to mitoxantrone and prednisone were comparable. Factors predictive of survival were similar in the 2 cohorts. Results of the randomized trial are generalizable to clinical practice.

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