Significance of serum free prostate specific antigen in the screening of prostate cancer

Purpose: The significance of serum free prostate specific antigen (PSA) in the screening of prostate cancer was examined. Materials and Methods: A prospective clinical trial was conducted on 701 male volunteers 50 years old or older. Serum free PSA was determined and biopsies were performed if PSA was greater than 4 ng./ml. or if digital rectal examination was suspicious for cancer. Results: Of the men 187 (27%) had a PSA of greater than 4 ng./ml. (11%) and/or a suspicious digital rectal examination (19%). Of 116 biopsies performed in the 701 men cancer was detected in 13 (1.9%). PSA detected more tumors (12 of 13, 92%) than digital rectal examination (9, 69%). Receiver operating characteristic analysis showed that the optimal free PSA-to-PSA ratio (free PSA ratio) was 12%. The positive predictive value for cancer according to PSA with free PSA ratio (50%, 10 cancers in 20 biopsies) was significantly greater (p = 0.0473) than that according to PSA alone (24%, 12 cancers in 50 biopsies), which indicated that 30 of 50 biopsies were avoided with only 2 cancers missed when PSA and free PSA were used for biopsy indication. Conclusions: Free PSA determination might eliminate unnecessary biopsies in men with a PSA of more than 4 ng./ml. with minimal missed cancers.