Prostate cancer screening within a prostate specific antigen range of 3 to 3.9 ng./ml.: a comparison of digital rectal examination and free prostate specific antigen as supplemental screening tests

Abstract

Purpose: Performing biopsy in all men with a serum prostate specific antigen (PSA) of 3 to 3.9 ng./ml. increases the sensitivity of prostate cancer screening compared with a PSA cutoff of 4 ng./ml. but decreases specificity and may contribute to over diagnosis. Therefore, we evaluated the detection rate and specificity attributable to digital rectal examination and percent free PSA within the PSA range of 3 to 3.9 ng./ml.

Materials and methods: Serum PSA was determined in 20,716 participants in the Finnish population based screening trial. Supplementary digital rectal examination was offered to men with a PSA of 3 to 3.9 ng./ml. during 1996 to 1998 (protocol 1). Those with a suspicious digital rectal examination finding were referred for biopsy. The screening algorithm was modified by substituting percent free PSA for digital rectal examination with a cutoff of 16% as a biopsy criterion in 1999 (protocol 2). In addition, biopsies were performed in all men with PSA 4 ng./ml. or greater.

Results: A total of 23 cancers (2.9%) were detected by digital rectal examination among 801 men, while percent-free PSA resulted in the diagnosis of 13 cases (4.8%) among 270 men with a PSA of 3 to 3.9 ng./ml. The detection rate of tumors with a Gleason score of 5 or greater increased from 1.6% (13 of 801 cases) to 4.4% (12 of 270) in the modified screening program. The PSA cutoff of 3 ng./ml. alone showed 88.6% and 87.5% specificity in protocols 1 and 2 but specificity increased to 93.3% and 91.7% using digital rectal examination and percent free PSA, respectively.

Conclusions: Using percent free PSA increased the detection rate of aggressive disease compared with digital rectal examination and provided higher specificity than PSA alone.