Perspectives on serum acid phosphatase in prostatic disease. An evaluation of two methods

Acid phosphatase in serum was measured in 116 patients with prostatic disease, benign in 59 and malignant in 57 cases. Comparisons were made between radioimmunoassay (RIA) and an enzymatic method. The correlation coefficient between the respective values was 0.96 in patients with untreated prostatic cancer, indicating that no significant difference between results with the two methods was to be expected. The correlation coefficient between RIA values and cancer stage was 0.48, and between catalytic activity and cancer stage it was 0.50. The validity of the two methods consequently was equal. RIA, however, was the more sensitive method, giving elevated values in 10 of 11 patients with untreated stage III or stage IV prostatic cancer, as compared with only 4 of the same 11 in the enzymatic assay. This seeming paradox most probably was attributable to differing intrinsic properties of the methods when the upper limits of normal range were established. Neither RIA nor enzymatic analysis discriminated early prostatic cancer (stages I and II) from benign lesions.