Bone marrow acid phosphatase in staging of prostatic cancer: how reliable is it?

To evaluate the reliability of bone marrow acid phosphatase in the staging of prostatic carcinoma we analyzed 50 bone marrow samples collected at random from the hematology service at this hospital. The samples were assayed for acid phosphatase content by a colorimetric method using sodium thymolphthalein monophosphate as a substrate and by 2 immunochemical assays developed at our laboratory (counter immunoelectrophoresis and radioimmunoassay). We found a high percentage (61 per cent) of falsely positive results in patients with various hematological diseases without evidence of prostatic carcinoma by the colorimetric evaluation. All of these patients except 1 had negative immunochemical assay. Until a specific assay for prostatic acid phosphatase is developed for clinical use we caution the use of a single elevation of bone marrow acid phosphatase as a parameter of metastatic disease.