A solid-phase fluorescent immunoassay for human prostatic acid phosphatase.

an aid in the diagnosis of prostate cancer since 1936 when Gutman et a!. (13) first reported the relationship between serum acid phosphatase and prostate cancer. They found that serum acid phosphatase activity markedly increased in patients with prostate carcinoma, especially in those with bone metastasis. Elevated serum acid phosphatase activity has been reported in 70 to 90% of the patients with metas tasized prostate cancer and in 5 to 30% of the patients who had no demonstrable metastasis (2, 20, 25). The serum acid phosphatase can also originate from platelets, leukocytes, RBC, and other tissues (26). Since diseases other than prostate cancer can also cause elevation of acid phospha tase activity (23, 26), it would be advantageous to develop a more specific assay method for the acid phosphatase of prostate origin. The effectiveness of treatment in prostate cancer and the survival rate of patients depends, as in other cancers, upon an early diagnosis. At an early stage of prostatic tumor growth, the amounts of acid phosphatase released into the blood stream from the prostate may be very low. A sensitive assay for detecting minute amounts of acid phosphatase of prostate origin will play an important role in early diagnosis of this cancer. However, the measurement of serum acid phosphatase by conventional spectrophotometric methods has failed to detect prostate cancer at its early stages (26). Recently, sensitive immunoassays have been reported for this enzyme by several investigators (4, 7, 8, 12). Although the counterimmunoebectrophoresis method is simpler, more sensitive, and more specific than the conventional spectrophotometric method for detecting serum prostatic acid phosphatase (7), it is, in practice, a semiquantitative method. The radioimmunoassay technique (4, 12) is a valuable quantitative method, but factors such as the ex pense of reagents, the potential health risks from isotope, and the instability of the labeled enzyme may limit its practical application. Therefore, we have developed a non isotope, solid-phase fluorescent immunoassay method for prostatic acid phosphatase in which a combination of immunological, biochemical, and chemical approaches is used. This assay is not only more sensitive but also elim mates the disadvantages of radioimmunoassay or counter immunoelectrophoresis. The technique is described in de tail in this report along with the preliminary results of this assay in cancer patients.