Isoenzymes of alkaline phosphatase - Useful parameters for identification of bone metastasis in prostatic carcinoma?

Background: The most frequent sites of metastases in prostatic carcinoma ar e bones. Bone scintigraphy is the diagnostic tool of first choice for stagi ng bone metastases in cancer of the prostate. But this examination is expen sive and time-consuming. Therefore we are looking especially for serum para meters like alkaline phosphatase, the isoenzyme of bone-specific alkaline p hosphatase, and prostate-specific antigen (PSA) to replace bone scintigraph y for diagnostic staging. Material and Method: We compared in 132 prostatic carcinoma patients the results of total alkaline phosphatase, bone-specifi c alkaline phosphatase, and PSA with the results of the bone scan. Results: All three parameters demonstrate a lower sensitivity compared to the bone s can. Although the highest specificity was obtained by bone-specific alkalin e phosphatase, this parameter cannot replace the bone scan for staging canc er of the prostate because of a lack of sensitivity. In a subgroup of patie nts with a PSA level below 10 ng/ml and a total alkaline phosphatase within normal range there is no need to obtain a bone scan, because of the very l ow incidence of bone metastasis in this group. Conclusions: There is only l ittle additional information if bone-specific alkaline phosphatase instead of total alkaline phosphatase is determined. None of the serum parameters e xamined can replace bone scintigraphy in staging cancer of the prostate, bu t PSA and alkaline phosphatase can identify patients who are at low risk fo r bone metastases.