Skeletal alkaline phosphatase in the metastatic workup of patients with prostate cancer

To compare the efficacy of two tests, prostate-specific antigen (PSA) and skeletal alkaline phosphatase (SAP) as staging markers to discriminate patients with cancer of the prostate (CaP) with bone metastases (M+) from those without bone metastases (M0).

Thirty-nine untreated patients with CaP M0 (n = 22) and CaP M+ (n = 17) along with 10 patients with benign prostatic hyperplasia, who served as controls, were entered in this study. Serum concentrations for SAP and PSA were determined using two immunoassays. Receiver operating characteristic (ROC) curves were constructed to compare the ability of SAP and PSA to discriminate patients with CaP M+ from CaP M0.

None of the M0 patients but 65% of the M+ patients exhibited an SAP value above the reference range (< 19 ng/ml). A corresponding cutoff point of 100 ng/ml for PSA demonstrated that 27% of M0 patients and only 65% of the M+ patients exhibited a value > 100 ng/ml. This resulted in a sensitivity of 65% for both markers. However, SAP revealed a higher specificity than PSA (100 vs. 73%). The ROC curve comparing SAP and PSA demonstrated the superiority of SAP as a marker for bone metastases.

Our findings suggest that SAP could become a useful marker in the evaluation of patients with newly diagnosed CaP as it seems to provide additional information concerning the skeletal status of these patients.