Clinical Significance of Measuring Free form of Prostate-Specific Antigen

Chung, Byung Ha; Hong, Sung Joon; Sung, Do Hwan; Mah, Sang Yol; Song, Jae Mann; Chung, Woo Sik; Shim, Bong Suk; Choi, Hak Ryong; Kwon, Sung Won

Abstract

Prostate-specific antigen(PSA) in serum exists in several molecular forms that can be measured by immunodetectable assays; free PSA, PSA complexed to alpha1-antichymotripsin and total PSA, which represents the sum of the free and complexed forms. We have determined the amount and ratio of these forms may be seful for increasing the ability of PSA to be used in distinguishing prostate cancer(PCa) from benign prostatic hyperplasia(BPH). We evaluated 117 asymptomatic healthy male controls(mean age 55.8, range 50-71) with no clinical evidence of PCa, 125 men with symptomatic BPH(mean age 67.6, range 52-89) who underwent prostatic surgery(open prostatectomy or TLRP) and 14 men with biopsy-proven, untreated PCa(mean age 71.3 range 54-86). Using ACS-PSA2 assay(Ciba-Corning). we measured the free PSA(F), total PSA(T) and free/total(F/T) ratio. The method utilized was monoclonal-polyclonal immunometric, chemiluminescent assay, using a standardized calibrator 90:10. We also performed total PSA measurement with Tandem-R PSA assay(Hybritech). Correlation between ACS-PSA2 assay and Tandem-RPSA assay was excellent (r2=0.93). Receivr operating characteristics(ROC) analyses between them showed very similar performances. ROC analysis of free to total PSA ratio was more superior than that of free form PSA only. When all subjects were included, the ratio of free to total PSA in controls, BPH and PCa were 0.27, 0.24 and 0.07, respectively. which significantly differentiated between PCa and benign conditions(p<0.01). When the cut-off value (Fr) was set into 0.12, its diagnostic sensitivity and specificity were 86% and 84%, respectively. These findings suggest that free to total PSA ratio may enhance the ability to distinguish benign histologic conditions from cancer.