ABSTRACT
PURPOSE: Prostate-specific antigen(PSA) exist in serum in two major immunodetectable molecular forms: free PSA, and complexed PSA(PSA- alpha-1-antichymotrypsin). Total PSA represents the sum of the free and complexedorms. Preliminary investigations have illustrated the potential benefits of using percent free PSA to enhance the utility of PSA in distinguishing benign prostate disease from prostate cancer. Our study was undertaken to define the effectiveness of precent free PSA in the early detection of prostate cancer and to determine appropriate cutoff points for percent free PSA in Korea when total PSA level is normal or mildly elevated so as to eliminate negative biopsies. MATERIALS AND METHODS: Patient samples consisted of 24 histologically confirmed primary cancer, 83 men with untreated benign prostate disease histologically confirmed by negative sextant biopsies, and 29 men with normal digital rectal examination and PSA values less than 4.0ng/ml. Total PSA and free PSA levels were determined using PSA-RIACT and FPSA-RIACT kit(Cis Bio International, France), respectively. Percent free PSA was calculated for all patients. Within the range of 2.5-20.0ng/ml, receiver operating curve(ROC) was generated and utilized to evaluate cutpoints for percent free PSA to be used in clinical practice. RESULTS: When all subjects were included, both total PSA and percent free PSA significantly discriminated patients with prostate cancer from patients with benign histologic conditions(p=0.0003 and p=0.0001, respectively). However, in men with total PSA values between 2.5 and 20.0ng/ml, the percent free PSA significantly discriminated patients with prostate cancer from patients with benign conditions(p=0.001), whereas the total PSA did not(p=0.14). Among this subgroup of patients, the analysis of sensitivity and specificity showed that the percent free PSA had a clearly higher specificity compared with that of the total PSA at the same level of sensitivity. Within the range of 2.5-20.0ng/ml, the cutoff point for percent free PSA was 20. CONCLUSIONS: Measurement of percent free PSA enhance the ability to discriminate prostate cancer from benign histologic condition while retaining high sensitivity for detecting cancer in men who present with total PSA levels between 2.5 and 20.0ng/ml.