Introduction: Prostate Specific Antigen (PSA) exists in the serum in several molecular forms which can be measured by immunoradiodetectable assays: free PSA and total PSA (which represent the sum of the free PSA and complexed PSA to alpha 1 antichymotrypsin). Recently, the proportion of free to total PSA could enhance the ability to distinguish benign histologic conditions from cancer.
Material and methods: Serum samples of 105 patients (31 histologically confirmed prostate cancers and 74 histologically confirmed untreated benign prostatic diseases) were included in this study. The total and free PSA levels were determined using the PSA immunoradioassay of Tandem-R PSA and Tandem - R free PSA.
Results: When all subjects were included, both total PSA and the proportion of free to total PSA significantly differentiated between patients with prostate cancer and patients with benign histologic conditions (p < 0.01 and p < 0.005). However, in men with total PSA values between 4.0 to 10.0 ng/ml, the proportion of free to total PSA significantly differentiated between the patients with benign and malignant histological conditions (p < 0.04). The most interesting was the ability of the proportion of free to total PSA to distinguish patients with total PSA value between 4.0 and 10.0 ng/ml and normal digital examination (p < 0.001). With these values of PSA-T, a free PSA cutoff of 0.23 detected at least 90.4% of cancers and would eliminate 19.4% of negative biopsies.
Conclusion: Measurement of the free to total PSA level improves specificity of prostate cancer screening in selected men with elevated total serum PSA levels between 4.0 to 10.0 ng/ml and normal digital examination, and can reduce unnecessary prostate biopsies with minimal effects on the cancer detection rate.