The value of acid phosphatase measurements in predicting extraprostatic cancer growth before radical prostatectomy

Acid phosphatase levels were determined using both an enzymatic method (32 cases) and radioimmunoassay (35 cases) in 35 patients with clinically localised prostatic cancer. All patients underwent total prostatectomy and pelvic lymphadenectomy. In cases of intracapsular prostatic cancer the level of prostatic acid phosphatase (PAP) measured by radioimmunoassay was 1.4 +/- 0.8 micrograms/l. In patients with either local extraprostatic disease or pelvic lymph node metastases the mean level of PAP was 3.5 +/- 2.8 micrograms/l. The difference was statistically significant. The specificity, sensitivity and accuracy of an elevated PAP (greater than 3.0 micrograms/l) in revealing extraprostatic extension of clinically localised prostatic cancer were 100, 37 and 66% respectively. When the enzymatic method was used, the level of acid phosphatase was elevated (greater than 13 u/l) in only 1 case. The specificity, sensitivity and accuracy of the enzymatic method were 100, 6 and 47% respectively. Elevation of PAP predicts, with a high degree of probability, either local extension outside the prostate or lymph node metastases. A normal PAP does not exclude extraprostatic extension of prostatic cancer.