Effectiveness of radioimmunoassay of human prostate-specific acid phosphatase in the diagnosis and follow-up of therapy in prostatic carcinoma.

The radioimmunoassay of human prostate-specific acid phosphatase and the measurement of the catalytic activity of acid phosphatase using p-nitrophenyl phosphate as substrate were compared in the diagnosis and follow-up of therapy of prostatic cancer patients. We monitored 17 patients without metastases and eight patients with metastases for 12 months. We detected elevation of the catalytic activity of acid phosphatase [the upper limit for the reference range was mean + 2 (S.D.)] in 24% of the sera of all these patients (n = 25), and the concentration of prostate-specific acid phosphatase measured by radioimmunoassay [the upper limit for the reference range was mean + 3 (S.D.)] was elevated in 80% of these samples before therapy. The radioimmunological measurement of prostate-specific acid phosphatase was therefore more efficient in detecting prostatic cancer than was measurement of the catalytic activity. Favorable effects of the various forms of endocrine treatment were detected more clearly by the measurement of immunoassayable prostatic acid phosphatase than by the measurement of catalytic activity. Activation of the disease during various forms of endocrine treatment of prostatic carcinoma is possibly more efficiently signaled by radioimmunoassay than by measurement of catalytic activity.