Clinical evaluation of a prostate-specific antigen as a serum marker of prostatic cancer

Combined measurement of serum prostate-specific antigen (PA) and prostatic acid phosphatase (PAP) was performed in 235 patients with various urologic diseases including 55 patients with prostatic cancer. A PA level of over 24.7 ng/ml and a PAP level of over 3.1 ng/ml were considered to be positive. The positive rate of PA was 57% in the patients with untreated prostatic cancer and 3% in the patients without prostatic cancer. The positive rate of PAP was 52% in the patients with untreated prostatic cancer and 1% in the patients without prostatic cancer. PA and PAP were considered to be equally sensitive and specific serum markers of prostatic cancer. However, the positive rate increased to 65% without increasing the false positive rate when the PA and PAP were both measured simultaneously. The combined assay of PA and PAP is recommended for screening prostatic cancer. The cross-over titer of PA and gamma-Sm using standard samples in each kit revealed linearity, which suggested that PA and gamma-Sm possess the same antigenicity.