Is prostate-specific antigen the most useful marker for screening in prostate cancer?

Analysis of variation in prostate-specific antigen values

This retrospective study analyzes variation in prostate-specific antigen (PSA) levels in 129 males who were not diagnosed with prostate cancer or other known malignancies. The extent to which the assay and the biologic variation contributed to the variation in PSA concentration was evaluated from analysis of slopes characterizing PSA concentration as a function of time. The mean coefficient of variation on observations was 58.0 percent. The estimated mean biologic coefficient of variation was 55.3 percent versus a mean assay coefficient of variation of 13.2 percent, indicating that the assay variation contributed negligibly to variation compared with the biologic variation. The concept that a PSA level which rises more than that attributable to assay variation indicates the need for invasive testing for prostate cancer is questionable. A decreasing PSA level was seen as often and of the same magnitude as an increasing level within a relatively narrow window of approximately one year. We are aware of no reason why this variability in PSA values would not be observed in patients with occult prostate cancer.

A prospective study of prostate specific antigen levels in patients receiving radiotherapy for localized carcinoma of the prostate

Prostate Specific Antigen (PSA) is becoming the preferred tumor marker in the management of prostate cancer. Prostate Specific Antigen levels fall exponentially after radical prostatectomy with a half-life of between 2 and 3 days. Persistently elevated Prostate Specific Antigen levels beyond 7 half-lives suggest occult residual disease and may serve as an indication for post operative adjunctive therapy. The change in Prostate Specific Antigen levels during a course of radical external beam radiotherapy for prostate cancer has not been described. In this study of 81 patients receiving radiotherapy for primary prostate cancer, 47 had elevated Prostate Specific Antigen levels prior to therapy and 35 had serial measurement of Prostate Specific Antigen during their course of treatment. Working on an assumption that in patients with radioresponsive localized prostate cancer Prostate Specific Antigen levels will fall exponentially during the radiotherapy, a half-life of 43 +/- 11 days was derived. Prostate Specific Antigen half-life appears independent of stage, grade, or pretreatment Prostate Specific Antigen level and may be an independent prognostic indicator. A prolonged Prostate Specific Antigen half-life may suggest untreated or resistant disease and serve as an indication for adjuvant hormonal treatment in patients receiving radiotherapy for primary prostate cancer.