Prostate Specific Antigen and Prostatic Acid Phosphatase for Monitoring Therapy of Carcinoma of the Prostate

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Abstract
Serial serum prostatic acid phosphatase (PAP) and prostate specific antigen (PSA) measurements were performed in 871 patients treated with hormonal combination therapy for stage C (95 patients) or stage D2 (776) prostate cancer for an average followup of 26 months. The relative efficacy of serum PAP and PSA for predicting recurrence of the disease was evaluated by 2 statistical methods at the time of progression as well as 6 and 12 months before clinical relapse of disease using optimized cut-off values of 2.0 and 4.0 micrograms/l. for serum PAP and PSA, respectively. At the time of progression the sensitivity (plus or minus standard deviation) of the 2 tests was estimated at 61.1 +/- 3.2% and 86.7 +/- 3.1% for PAP and PSA, respectively, while the specificity (plus or minus standard deviation) was calculated at respective values of 79.6 +/- 1.3% and 92.4 +/- 4.1%. Receiver operating characteristic analysis disclosed a greater accuracy for PSA at 89.2 +/- 1.7% versus 78.7 +/- 1.6% (plus or minus standard deviation) for PAP. The somewhat lower positive predictive value of the PSA test (81.4% versus 89.6%) is more than compensated by its superior negative predictive value (92.4% versus 79.6%). The present data also show that serum PSA measurements are superior to those of serum PAP for predicting disease recurrence in stages C and D prostate cancer patients treated by combination endocrine therapy and they indicate that measurement of serum PAP does not add significantly to single measurement of serum PSA alone.