PSP94: Evaluation of Prognostic Utility in Patients Treated with Radiotherapy for Nonmetastatic Prostate Cancer

Objectives: Conflicting reports exist as to the utility of PSP94 in the diagnosis and management of prostate cancer. We have identified serum-bound forms of PSP94 in prostate cancer patients. To further evaluate the usefulness of this finding, we measured bound and free serum PSP94 levels in patients with nonmetastatic prostate cancer before radiotherapy. Materials and Methods: Pretreatment levels of free PSP94 in 42 patients were measured in serum via a competitive enzyme-linked immunosorbent assay. Levels of bound PSP94 were measured by a semiquantitative assay after fractionation of total serum proteins by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and Western blot analysis. Pretreatment levels of prostate specific antigen (PSA) were measured by a commercially available assay. Archival sera from 42 patients and a subgroup of 27 patients with “favorable” pretreatment PSA values (i.e., < 10 ng/ml) were statistically analyzed. Pretreatment levels of PSP94 (free and bound) and PSA, as well as tumor stage and grade, were correlated with treatment outcome (biochemical relapse-free survival) postradiotherapy. Results: Pretreatment PSA and the ratio of bound to free PSP94 were significant predictors of relapse postradiotherapy on univariate analysis. An elevated ratio of bound to free PSP94 was a stronger predictor (p = 0.0074) of relapse postradiotherapy compared with PSA level (p = 0.070) in a subgroup of prostate cancer patients with “favorable” pretreatment PSA levels. Conclusions: The results presented here indicate that serum PSP94-bound complexes must be considered in evaluating the clinical utility of PSP94 as a prostate cancer marker. A higher ratio of bound to free PSP94 may indicate worse outcome postradiotherapy. Differential testing of serum PSP94 has shown that it, in addition to PSA, may be of prognostic value for patients receiving radiotherapy for nonmetastatic prostate cancer.