Prostate carcinoma staging. Clinical utility of bone alkaline phosphatase in addition to prostate specific antigen

BACKGROUND: Biochemical markers of bone disease have been of interest as part of the investigation of prostate carcinoma and the monitoring of skeletal involvement. Bone isoenzyme of the alkaline phosphatase (BAP) is an indicator of the metabolism of the osteoblasts. An immunoradioanalyses with two monoclonal antibodies in sandwich was developed, allowing an accurate measurement of BAP concentration. The goal of the current study was to compare the clinical performance of BAP and prostate specific antigen (PSA) in patients with untreated prostate carcinoma and to determine whether or not BAP can provide valuable additional information to PSA regarding the degree of skeletal extension in patients with prostate carcinoma. METHODS: BAP and PSA serum concentrations were determined in 140 newly diagnosed prostate carcinoma patients (72 M0 and 68 M1-4). The efficiency of both markers in the prediction of positive bone scans was studied as well as the relationship observed between the concentrations of the two markers and the degree of skeletal involvement. To investigate the potential utility of BAP and PSA in eliminating the need for a bone scan, the negative predictive values for different cutoff points for both markers were calculated. RESULTS: BAP was more efficient than PSA in the prediction of positive bone scans and its level was significantly related to the magnitude of skeletal involvement whereas PSA was only able to distinguish between M0 and M1-4 groups of patients. The highest predictive value for a bone scan result was found for BAP cutoff values between 20 and 30 ng/mL, leading to negative and positive predictive values of 92.6% and 98.2%, respectively. The combination of BAP and PSA both set at a 20 ng/ mL cutoff value yielded a negative predictive value of 100% and the combination of BAP and PSA at 30 ng/mL and 20 ng/mL cutoff values, respectively, increased the positive predictive value to 98.5%. CONCLUSIONS: This study suggests that BAP could be a complementary marker to PSA in the diagnosis of bone disease in patients with prostate carcinoma. Its clinical utility could result in important cost saving implications, eliminating bone scan when PSA ranges from 10 to 20 ng/mL because the predictive negative value of PSA < 20 ng/mL and BAP < 20 ng/mL is 100% in this series. In addition, it could provide useful clinical information regarding the degree of skeletal involvement.