Monitoring of prostatic cancer by an enzyme-linked immunosorbent assay of serum prostatic acid phosphatase.
A longitudinal study of serum prostatic acid phosphatase (sPAP) in 167 cases of carcinoma of the prostate was made using an enzyme-linked immunosorbent assay. The sensitivity of the assay was valuable in accurately exploring the low levels of sPAP achieved after treatment by orchidectomy or oestrogens. For the majority of patients with metastatic disease, treatment resulted in the level of sPAP falling to normal within 3-9 months, but in about half of these patients the level of sPAP had begun to increase again, exponentially, within 2 years. This exponentially rising level of sPAP was well correlated with evidence of progression as indicated by bone scans. The rise of sPAP in M1 disease could not be accounted for by an attenuation of the suppression of testosterone. After hormone manipulation in M0 disease the sPAP generally fell to below 1.5 ng/ml and remained at this level for the duration of the study. In untreated M0 disease there were small fluctuations in the level of sPAP, and it had a higher baseline level. In both treated and untreated patients a rising level of sPAP above normal tended to indicate tumour progression.