Will Prostatic Acid Phosphatase Determination by Radioimmunoassay Increase The Diagnosis of Early Prostatic Cancer?

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Abstract
The determination of serum prostatic acid phosphatase by radioimmunoassay has received considerable attention as a more sensitive and specific test than its measurement by the usual enzymatic assay. The increased sensitivity of the radioimmunoassay probably will greatly improve the ability to diagnose prostatic cancer in the early operative stages. Prostatic acid phosphatase determination by the radioimmunoassay and enzymatic techniques were compared in 56 untreated and treated patients with prostatic cancer. Patients (22) with biopsy-proved benign prostatic hyperplasia were also studied. The radioimmunoassay used was based on antibodies raised against prostatic acid phosphatase highly purified by 2-stage, ion-specific chromatography and isoelectric focusing techniques. The enzymatic assay used thymolphthalein monophosphate as the substrate. The patients were staged on the basis of digital examination, Tc bone scan and pelvic lymphadenectomy. There were 4 patients with stage A, 12 with stage B, 13 with stage C and 27 with stage D disease. The radioimmunoassay showed an elevated prostatic acid phosphatase in 13% of the patients with intracapsular disease (stages A and B) and in 50% of the patients with extracapsular disease (stages C and D). This finding compares with an enzymatic prostatic acid phosphatase elevation in 13% of the patients with intracapsular and 53% of those with extracapsular disease. There were fewer falsely elevated prostatic acid phosphatase levels by radioimmunoassay (2) than by enzymatic assay (6) in the patients with benign prostatic hyperplasia. The radioimmunoassay method apparently provides a reliable and specific measurement of prostatic acid phosphatase. The radioimmunoassay measurement of prostatic acid phosphatase does not appear to be more effective as a screening aid in the diagnosis of early stages of prostatic cancer; it was no more helpful than the enzymatic assay.