Prostate-specific antigen as a measure of disease outcome in metastatic hormone-refractory prostate cancer.

PURPOSE: To evaluate the prognostic significance of pretreatment parameters and posttherapy declines in prostate-specific antigen (PSA) in relation to the survival of patients with hormone-refractory prostate cancer. PATIENTS AND METHODS: One hundred ten assessable patients treated on seven sequential protocols at Memorial Sloan-Kettering Cancer Center (MSKCC) for hormone-refractory prostate cancer were evaluated for 29 different pretherapy and posttherapy parameters, including a posttherapy decline in PSA of 50% and 80% from baseline. RESULTS: In the univariate analysis, initial Karnofsky performance status (KPS) > or = 80% was associated with a favorable outcome (P = .005), while age, extent of disease on bone scan, and individual sites of metastatic disease were not significant. No difference in survival was observed between patients with measurable or assessable (bone only) disease. Initial hemoglobin (HGB; P = .0012), alkaline phosphatase (ALK; P = .0015), and lactate dehydrogenase (LDH; P = .0002) levels were significant discriminators, while the initial PSA was not. Using a landmark analysis, a significantly longer median survival rate was observed for patients with a > or = 50% decline in PSA (median not reached) versus patients with a less than 50% decline in PSA (median, 8.6 months; P = .0001). Multivariate analysis using the Cox proportional hazards model showed that a > or = 50% decline in PSA (P = .0004) and the natural log of LDH (P = .0001) were the two most significant variables predicting survival. The model was confirmed on an independent data set from the Norwegian Radium Hospital (NRH) in Oslo, Norway. CONCLUSION: The results suggest that posttherapy PSA declines can be used as a surrogate end point to evaluate new agents in hormone-refractory prostate cancer. The criteria for response need prospective validation in phase III trials.