THE ROLE OF SERUM PROSTATIC ACID-PHOSPHATASE IN THE MANAGEMENT OF ADENOCARCINOMA OF THE PROSTATE WITH RADIOTHERAPY

Between 1974 and 1983, 472 patients with clinically-staged adenocarcinoma of the prostate treated by radiotherapy had baseline and follow-up prostatic acid phosphatase (SPAP) measurements by the enzymatic Roy method. The mean pretreatment SPAP was higher in Stage C (0.65 mIU/ml) than in combined Stages A2/B (0.43 mIU/ml), (p < 0.05). Likewise, the incidence of elevated SPAP (> 0.8 mIU/ml) was also higher in Stage C (12%) than in Stages A2/B (3%), (p < 0.01). Only 3 of 113 patients in Stages A2/B had an elevated SPAP and all three remain disease-free. In Stage C elevated SPAP was an adverse prognostic factor, and patients with a normal SPAP fared worse if their value was in the upper half of normal (> 0.4 mIU/ml) rather than in the lower half (less-than-or-equal-to 0.4 mIU/ml). However, in Stage C, tumor grade was found to correlate with initial SPAP, so that the higher the grade, the higher was the mean SPAP and the greater was the incidence of elevated SPAP. When stratified for grade, the prognostic significance of low-normal versus high-normal SPAP in Stage C was lost. An elevated SPAP was, however, an independent adverse prognostic factor for patients with intermediate and high grade tumors. Following radiotherapy, mean SPAP values fell significantly within 1-3 months. For patients with initially normal SPAP, this fall was of no prognostic significance. In 80% of the patients with baseline elevation of SPAP, the values normalized following treatment and the relapse rate in these patients was 51%, which was still higher than the relapse rate of patients with initially normal SPAP (33%) (p < 0.05) but was lower than the 89% relapse rate in patients whose post-radiation SPAP did not normalize (p < 0.05). Pretreatment SPAP was of independent prognostic significance for only 6% of the study population and therefore has quite limited usefulness in the management of this disease. SPAP decreases following radiotherpay, but this is of prognostic significance only for the small group of patients with elevated pretreatment values.