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.