Prostate specific antigen (PSA) value adjusted for transition zone volume and free PSA (gamma-seminoprotein)/PSA ratio in the diagnosis of prostate cancer in patients with intermediate PSA levels.

Abstract

To determine: (i) whether the accuracy of prostate-specific antigen (PSA) density is improved by using the transition zone (TZ) volume instead of total prostate volume, with the gamma-seminoprotein (gamma SP, a measure of free PSA) to total PSA ratio, for detecting prostate cancer; and (ii) to assess the influence of prostate volume on PSA density and gamma SP/PSA ratio. From April 1995 to July 1997, 297 consecutive patients (46-88 years old) were examined; all had intermediate serum PSA levels (4-10 ng/mL) and/or abnormal findings on digital rectal examination. All patients underwent transrectal ultrasonography (TRUS)-guided biopsy, and the prostate and TZ volumes determined from TRUS. The PSA density relative to the total prostate volume (PSAD) and to the TZ volume (PSAT) were then calculated. The total PSA and gamma SP levels were measured before the diagnostic procedures. Of the 297 patients, 62 (21%) were histologically confirmed to have prostate cancer by biopsy. The area under the receiver operating characteristic curve was 0.680 for PSA, 0.684 for PSAD, 0.764 for PSAT, 0.748 for gamma SP/PSA, 0.885 for gamma SP/PSA in patients with a prostate volume < 40 mL, while it was 0.817 for PSAT in patients with a prostate volume of > or = 40 mL. Using a PSAT threshold of 0.17 in patients with a prostate volume of 40 mL, the number of biopsies was reduced by 56% (66 of 118) and 22 of the 25 cancers (88%) were detected. In addition, a gamma SP/PSA ratio threshold of 40% in patients with a prostate volume of < 40 mL decreased the number of biopsies by 75% (88 of 117) and detected 32 of the 37 cancers (87%). Prostate volume was significantly and positively correlated with gamma SP/PSA and negatively correlated with PSAT. Among patients with a PSA level of 4-10 ng/mL, a low gamma SP/PSA was most useful for detecting prostate cancer when the prostate volume was < 40 mL and a high PSAT was useful when the prostate volume was > or = 40 mL.