Re-examining the role of prostate-specific antigen density in predicting outcome for clinically localized prostate cancer

Objectives. To evaluate the prognostic significance of prostate-specific antigen density (PSAD) in clinically localized prostate cancer and determine whether this index is independent of or superior to prostate-specific antigen (PSA) in predicting outcome of patients treated with external beam radiotherapy. Methods. Between January 1989 and December 1995, 175 evaluable patients with clinically localized prostate cancer received definitive radiotherapy using computed tomography (CT)-guided conformal techniques. PSAD was defined as the ratio of the pretreatment serum PSA to the prostate volume measured from CT treatment planning scans by one investigator. All PSA values were determined using the Hybritech assay. Biochemical failure was defined as two consecutive elevations in PSA separated by at least 3 months and a final PSA value greater than 1 ng/mL. Results. Multivariate analysis including PSA and Gleason score revealed both to be statistically significant predictors of biochemical disease-free survival (P = 0.048 and P <0.001, respectively). PSAD did not achieve significance on regression analysis. A direct multivariate analysis including PSA and PSAD required dichotomization in order to reduce high correlation. This analysis demonstrated a relative risk (RR) for failure of 1.27 (NS) for high PSA versus low PSA compared with a RR of 1.20 (NS) for high PSAD versus low PSAD. A regression model containing all three variables indicated only the Gleason score as significant in predicting biochemical failure. Conclusions. These data do not suggest that PSAD is either an independent prognostic factor or a stronger discriminant of outcome than PSA in patients with clinically localized prostate cancer treated with definitive external beam radiotherapy. Larger patient numbers with longer follow-up data, use of a clinical end point, or an analysis restricted to the appropriate subgroup may demonstrate the utility of PSAD in the future. (C) 1997, Elsevier Science Inc. All rights reserved.