The role of serum prostatic acid phosphatase as a tumor marker in men with advanced adenocarcinoma of the prostate.

Serial serum prostatic acid phosphatase levels were obtained every 4 hours during a 48-hour interval from 10 men with stage D adenocarcinoma of the prostate. No therapeutic or diagnostic manipulations occurred during sample procurement, so that the amount of fluctuation of serum prostatic acid phosphatase levels that can be expected in these patients could be determined. The coefficient of variation for each man ranged from 16.67 to 43.68 per cent, which was significantly higher than the expected 8 per cent coefficient of variation determined with a control sample. The maximum percentage variations above and below the mean were 79 and 50 per cent, respectively. The average percentage variation in all patients was within 50 per cent greater than and 50 per cent less than the mean value of prostatic acid phosphatase. Thus, the usefulness of serum acid phosphatase by radioimmunoassay as a clinical tumor marker is limited by the number of serial assays needed to establish a mean. Based on these findings, certain guidelines are suggested.