The potential of the percentage of free (unbound) PSA to total PSA (usually abbreviated to %fPSA) as a measure to assist in the analysis of risk for prostate cancer has been known for years. However, researchers at the Cleveland Clinic thought it might be a good idea to check on that potential in an era of 10- and 12-core biopsies (compared the sextant biopsies customary in the early to mid 1990s).
Lee et al. have assessed data from 1,077 men who had had their %fPSA measured (as well as their total serum PSA) and who had undergone an initial extended prostate biopsy.
The men were divided into two groups based on their total serum PSA levels:
- Group A was made up of the men with a total serum PSA level >4.0 ng/ml.
- Group B included only men with a total PSA level ≤ 4.0 ng/ml.
The results of the analysis showed that:
- Cancer was detected in 453/1,077 patients (42.1 percent).
- The average (mean) PSA level among all patients was 7.6 ng/ml.
- The average (mean) %fPSA was 18.0 percent.
- The ability of %fPSA to predict prostate cancer on initial extended biopsy was significantly better in Group B than in Group A.
- For men in Group B, a %fPSA level of 11 percent or less was 85 percent specific for a positive biopsy result.
- For men in Group A, a %fPSA level of 10 percent or less was 85 percent specific for a positive biopsy result.
Lee et al. conclude that the performance of %fPSA in predicting the presence of prostate cancer is not altered when an extended biopsy scheme was used compared to the older sextant biopsy. They are careful to note that a %fPSA level higher than 10 or 11 percent can not be used to rule out the possibility of a biopsy result that is positive for prostate cancer. However, they also note that a low %fPSA value is likely to be particularly useful in predicting prostate cancer — especially in men who may have a PSA level < 4 ng/ml and no indication of potentially cancerous tissue on digital rectal examination.