A solid phase radioimmunoassay for prostatic acid phosphatase

The sensitivity of a recently developed solid phase radioimmunoassay for human prostatic acid phosphatase was compared to that of an enzymatic method using p-nitrophenylphosphate as substrate. In 109 histologically verified untreated stages I to IV prostatic cancers and 200 men without such cancer the solid phase radioimmunoassay method demonstrated substantially greater sensitivity and specificity than the enzymatic technique. In the 109 prostatic malignancies the immunochemical method correctly classified 80 (73 per cent) versus 34 (31 per cent) for the p-nitrophenylphosphate enzymatic technique (p less than 10(-6). In 44 stages I and II cancers confined to the prostate the radioimmunoassay was abnormally elevated in 19 (43 per cent) with only 4 (9.1 per cent) enzymatic elevations (p less than 10(-3). In 65 stages III and IV extraprostatic cancers correct classifications were noted in 61 (94 per cent) of the radioimmunoassays and 30 (46 per cent) enzymatic tests (p less than 10(-6). The radioimmunoassay in 200 male controls yielded 11 (5.6 per cent) and the p-nitrophenylphosphate enzymatic test yielded 7 (3.5 per cent) falsely positive results. In 90 non-prostatic human cancer sera 85 (94.5 per cent) were correctly classified as negative by the radioimmunoassay for prostatic acid phosphatase versus 66 (73 per cent) as negative by the enzymatic method. These data are discussed in terms of the merits of a radioimmunochemical approach for the measurement of human serum prostatic acid phosphatase.