REEXAMINING THE ROLE OF PROSTATE-SPECIFIC ANTIGEN DENSITY IN PREDICTING OUTCOME FOR CLINICALLY LOCALIZED PROSTATE-CANCER

Objectives. To evaluate the prognostic significance of prostate-specif ic 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 Decembe r 1995, 175 evaluable patients with clinically localized prostate canc er received definitive radiotherapy using computed tomography (CT)-gui ded conformal techniques. PSAD was defined as the ratio of the pretrea tment serum PSA to the prostate volume measured from CT treatment plan ning scans by one investigator. All PSA values were determined using t he Hybritech assay. Biochemical failure was defined as two consecutive elevations in PSA separated by at least 3 months and a final PSA valu e greater than 1 ng/mL. Results. Multivariate analysis including PSA a nd Gleason score revealed both to be statistically significant predict ors of biochemical disease-free survival (P = 0.048 and P <0.001, resp ectively). PSAD did not achieve significance on regression analysis. A direct multivariate analysis including PSA and PSAD required dichotom ization in order to reduce high correlation. This analysis demonstrate d a relative risk (RR) for failure of 1.27 (NS) for high PSA versus lo w 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 Gl eason score as significant in predicting biochemical failure. Conclusi ons. These data do not suggest that PSAD is either an independent prog nostic factor or a stronger discriminant of outcome than PSA in patien ts with clinically localized prostate cancer treated with definitive e xternal beam radiotherapy. Larger patient numbers with longer follow-u p 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.