Clinical evaluation of serum prostate-specific antigen-apha₁-antichymotrypsin complex values in diagnosis of prostate cancer: A cooperative study

Background: We studied the clinical significance of serum prostate-specific antigen bound to α₁-antichymotrypsin (PSA-ACT) values determined with a newly developed enzyme immunoassay. Methods: Serum PSA-ACT values were determined in a total of 652 sera. Clinical utility for the diagnosis of prostate cancer was compared to that of Tandem-RPSA and γ-seminoprotein (γ-Sm). The new enzyme immunoassay is based on the use of the Stanford reference as an international standard for PSA assays. Results: Serum PSA-ACT values ranged from less than 0.10 to 1.4 ng/mL in healthy males (n = 100) while values in patients with benign prostatic hyperplasia (n = 155) averaged 3.4 ± 3.8 ng/mL (mean ± SD). In patients with prostate cancer, serum PSA-ACT values increased significantly with progression of the clinical stage and there were statistically significant differences between benign prostatic hyperplasia and each stage of prostate cancer except for stage A. Using BPH levels as controls (4.8 ng/mL for PSA-ACT, 7.2 ng/mL for PSA, 3.8 ng/mL for γ-Sm, and 2.4 ng/mL for the complexed/free PSA ratio of PSA-ACT/γ-Sm), specificity was 80%. The sensitivity of prostate cancer detection was 79% for PSA-ACT, 77% for PSA, 57% for γ-Sm, and 46% for the ratio between PSA-ACT/γ-Sm. Conclusion: Although the determination of serum PSA-ACT showed essentially the same utility as that of PSA for the diagnosis of prostate cancer, PSA-ACT may allow prediction of the clinical stage. The PSA-ACT assay may therefore replace PSA in the detection of prostate cancer.